Old English denn "wild animal's lair, hollow place in the earth used by an animal for concealment, shelter, and security," from Proto-Germanic *danjan (source also of Middle Low German denne "lowland, wooded vale, den," Old English denu "valley," Old Frisian dene "down," Old High German tenni, German tenne "threshing floor," perhaps from a PIE word meaning "low ground").

Transferred to den-like places in human habitations in Middle English: "secret lurking place of thieves, place of retreat" (late 13c.); "apartment, private chamber" (late 14c.), but the modern use for "small room or lodging in which a man can seclude himself for work or leisure" [OED] is a modern development, originally colloquial, attested by 1771. By 1956, however, at least in U.S., the den had come to be a sort of family all-purpose room. In 19c. it also often had a bad sense, "a haunt, squalid place of retreat" (as in the set phrase den of iniquity for a brothel, etc.).

For, in truth, without a den or place of refuge, a man can achieve neither tranquility nor greatness. Jefferson wrote the Declaration of Independence in a quiet rooming house in Philadelphia. The soaring ideas that went into it evolved during hours of reading and contemplation in a secluded library. Had it been a study-TV-guest-family room, the United States might still be a colony. [The Kiplinger Magazine, September 1956]

1596, in reference to the famous London prison, on the site of one of the seven gates in the old London wall (the main gate to the west); this one having been used as a lock-up since the 1100s. So called because it was thought to be more recent than the others (but it apparently dated to Roman times) or because it had been rebuilt at some point. The gate was demolished in the 18c.; the last prison of that name was torn down 1902-3.

Newgate frill, "a beard shaved so as to grow only under the chin and jaw," so called in allusion to the position of the hangman's noose, is by 1851. The author of "The Habits of Good Society" (1859) calls it "a kind of compromise between the beard and the razor."

Both Coleridge and Ruskin praised Thomas Hood's Newgatory.

Hood was addressing the admirable Mrs. Fry, who, as every one knows, set up a school in Newgate to teach the poor neglected outcasts what they had never heard from Christian lips before. One of the chief points made by Hood is this,—how much better, kinder, wiser, more politic even, it would be to multiply these schools outside, not inside the Prison walls, so that prevention might take the place of cure. [Alfred Ainger, preface to "Humorous Poems by Thomas Hood"]

As a literary study, this exquisite pun of Hood's ... deserves the most careful memory, as showing what a noble and instructive lesson even a pun may become, when it is deep in its purpose, and founded on a truth which is perfectly illustrated by the seeming equivocation. [Ruskin, "Fors Clavigera"]

Middle English reden, ireden, "to counsel, advise," also "to read," from Old English rædan, gerædan (West Saxon), redan, geredan (Anglian) "to advise, counsel, persuade; discuss, deliberate; rule, guide; arrange, equip; forebode; to read (observe and apprehend the meaning of something written), utter aloud (words, letters, etc.); to explain; to learn through reading; to put in order."

This is reconstructed to be from Proto-Germanic *redan, source also of Old Norse raða, Old Frisian reda, Dutch raden, Old High German ratan, German raten "to advise, counsel, interpret, guess," from PIE root *re- "to reason, count."

Cognate words in most modern Germanic languages still mean "counsel, advise" (compare rede). Old English also had a related noun ræd, red "advice," and read is connected to riddle (n.1) via the notion of "interpret." Century Dictionary notes that the past participle should be written red, as it formerly was, and as in lead/led. Middle English past participle variants include eradde, irad, ired, iræd, irudde.  

The sense-transference to "interpret and understand the meaning of written symbols" is said to be unique to English and (perhaps under Old English influence) Old Norse raða. Most languages use a word rooted in the idea of "gather up" as their word for "read" (such as French lire, from Latin legere).

Sense of "make out the character of (a person)" is attested from 1610s. Musical sense of "perform (at first sight) from the notes" is by 1792. To read up "systematically study" is from 1842; read out (v.) "expel by proclamation" (Society of Friends) is from 1788. Read-only in computer jargon is recorded from 1961.

"medieval chemistry; the supposed science of transmutation of base metals into silver or gold" (involving also the quest for the universal solvent, quintessence, etc.), mid-14c., from Old French alchimie (14c.), alquemie (13c.), from Medieval Latin alkimia, from Arabic al-kimiya, from Greek khemeioa (found c.300 C.E. in a decree of Diocletian against "the old writings of the Egyptians"), all meaning "alchemy," and of uncertain origin.

Perhaps from an old name for Egypt (Khemia, literally "land of black earth," found in Plutarch), or from Greek khymatos "that which is poured out," from khein "to pour," from PIE root *gheu- "to pour" [Watkins, but Klein, citing W. Muss-Arnolt, calls this folk etymology]. The word seems to have elements of both origins.

Mahn ... concludes, after an elaborate investigation, that Gr. khymeia was probably the original, being first applied to pharmaceutical chemistry, which was chiefly concerned with juices or infusions of plants; that the pursuits of the Alexandrian alchemists were a subsequent development of chemical study, and that the notoriety of these may have caused the name of the art to be popularly associated with the ancient name of Egypt. [OED]

The al- is the Arabic definite article, "the." The art and the name were adopted by the Arabs from Alexandrians and entered Europe via Arabic Spain. Alchemy was the "chemistry" of the Middle Ages and early modern times, involving both occult and natural philosophy and practical chemistry and metallurgy. After c. 1600 the strictly scientific sense went with chemistry, and alchemy was left with the sense "pursuit of the transmutation of baser metals into gold, search for the universal solvent and the panacea."

"1 more than three, twice two; the number which is one more than three; a symbol representing this number;" Old English feower "four; four times," from Proto-Germanic *fedwores (source also of Old Saxon fiuwar, Old Frisian fiower, fiuwer, Frankish *fitter-, Dutch vier, Old High German fior, German vier, Old Norse fjorir, Danish fire, Swedish fyra, Gothic fidwor "four"), from PIE root *kwetwer- "four." The phonetic evolution of the Germanic forms has not been fully explained; Watkins explains the -f- as being from the following number (Modern English five).

To be on all fours is from 1719; earlier on all four (14c.). Four-letter word as a euphemism for one of the short words generally regarded as offensive or objectionable is attested from 1923; four-letter man is recorded from 1920 (apparently as a euphemism for a shit). Compare Latin homo trium litterarum, literally "three-letter man," a euphemism for fur "a thief." A four-in-hand (1793) was a carriage drawn by four horses driven by one person; in the sense of "loosely tied necktie" it is attested from 1892. To study The History of the Four Kings (1760, compare French Livres des Quatre Rois) contains an old euphemistic slang phrase for "a pack of cards," from the time when card-playing was considered a wicked pastime for students. Slang 4-1-1 "essential information" (by 1993) is from the telephone number called to get customer information. The four-color problem so called from 1879. The four-minute mile was attained 1954.

c. 1300, "onward movement, motion forward, a running in a prescribed direction or over a prescribed distance; path or distance prescribed for a race, a race-course" from Old French cors "course; run, running; flow of a river" (12c.), from Latin cursus "a running; a journey; direction, track navigated by a ship; flow of a stream;" from curs- past participle stem of currere "to run" (from PIE root *kers- "to run").

Also from c. 1300 as "order, sequence;" meanings "habitual or ordinary procedure" (as in course of nature) and "way of life, personal behavior or conduct" are from early 14c.

Most of the extended senses developed 14c. from notion of "line in which something moves" (as in hold one's course) or "stage through which something must pass in its progress." Thus, via the meaning "series or succession in a specified or systematized order" (mid-14c.) comes the senses of "succession of prescribed acts intended to bring about a particular result" (c. 1600, as in course of treatment) and the academic meaning "planned series of study" (c. 1600; in French from 14c.), also "that part of a meal which is served at once and separately" (late 14c.).

Meaning "the flow of a stream of water" is from mid-14c.; that of "channel in which water flows" is from 1660s. Courses was used for the flow of bodily fluids and 'humors' from late 14c.; specifically of menstrual flux from 1560s.

Adverbial phrase of course "by consequence, in regular or natural order" is attested from 1540s, literally "of the ordinary course;" earlier in the same sense was bi cours (c. 1300). Matter of course "something to be expected" is by 1739.

1520s, "oblique or diagonal line," from French biais "a slant, a slope, an oblique," also figuratively, "an expedient, means" (13c., originally in Old French a past-participle adjective, "sideways, askance, against the grain"), a word of unknown origin. Probably it came to French from Old Provençal biais, which has cognates in Old Catalan and Sardinian, and is possibly via Vulgar Latin *(e)bigassius from Greek epikarsios "athwart, crosswise, at an angle," from epi "upon" (see epi-) + karsios "oblique" (from PIE *krs-yo-, suffixed form of root *sker- (1) "to cut").

In the old game of bowls, it was a technical term used in reference to balls made with a greater weight on one side, causing them to curve obliquely (1560s); hence the figurative use "a one-sided tendency of the mind" (1570s), and, at first especially in law, "undue propensity or prejudice."

The bias of education, the bias of class-relationships, the bias of nationality, the political bias, the theological bias—these, added to the constitutional sympathies and antipathies, have much more influence in determining beliefs on social questions than has the small amount of evidence collected. [Herbert Spencer, "The Study of Sociology," 1873]

For what a man had rather were true he more readily believes. Therefore he rejects difficult things from impatience of research; sober things, because they narrow hope; the deeper things of nature, from superstition; the light of experience, from arrogance and pride, lest his mind should seem to be occupied with things mean and transitory; things not commonly believed, out of deference to the opinion of the vulgar. Numberless in short are the ways, and sometimes imperceptible, in which the affections colour and infect the understanding. [Francis Bacon, "Novum Organum," 1620]

late 14c., "calculation and foretelling based on observation of heavenly bodies," from Latin astrologia "astronomy, the science of the heavenly bodies," from Greek astrologia "astronomy," literally "a telling of the stars," from astron "star" (from PIE root *ster- (2) "star") + -logia "treating of" (see -logy).

Originally identical with astronomy and including scientific observation and description. The special sense of "astronomy applied to prediction of events" was divided into natural astrology "the calculation and foretelling of natural phenomenon" (tides, eclipses, dates of Church festivals, etc.), and judicial astrology "the art of judging occult influences of stars and planets on human affairs."

In Latin and later Greek, astronomia tended to be more scientific than astrologia.  In English, the differentiation between astrology and astronomy began late 1400s and by late 17c. this word was limited to the sense of "reading influences of the stars and their effects on human destiny."

And consequently, an Astrology in the World before Astronomy, either in Name or Science. so that (Non obstante whatever any Astronomer shall oppose to the contrary) Astrology hath the right of Primogeniture. And all the Sober and Judiciously Learned must needs acknowledge the Truth hereof.—Howbeit, it were to be wished that the Astrologer understood Astronomy, and that the Astronomer were acquainted with Astrology: Although I do in truth despair of ever finding many to be so happily Accomplished. [John Gadbury, introduction to "Ephemerides of the Celestial Motions," London, 1672]

It is ... an extremely just observation of M. Comte, that [the study of astrology] marks the first systematic effort to frame a philosophy of history by reducing the apparently capricious phenomena of human actions within the domain of law. It may, however, I think, be no less justly regarded as one of the last struggles of human egotism against the depressing sense of insignificance which the immensity of the universe must produce. [W.E.H. Lecky, "History of the Rise and Influence of the Spirit of Rationalism in Europe," 1866] 

mid-14c., "a plotting of evil, unlawful design; a combination of persons for an evil purpose," from Anglo-French conspiracie, Old French conspiracie "conspiracy, plot," from Latin conspirationem (nominative conspiratio) "agreement, union, unanimity," noun of action from past-participle stem of conspirare "to agree, unite, plot," literally "to breathe together" (see conspire).

Earlier in same sense was conspiration (early 14c.), from French conspiration (13c.), from Latin conspirationem. An Old English word for it was facengecwis.

Conspiracy theory "explanation of an event or situation involving unwarranted belief that it is caused by a conspiracy among powerful forces" emerged in mid-20c. (by 1937) and figures in the writings of, or about, Charles Beard, Hofstadter, Veblen, etc., but the degree of paranoia and unreasonableness implied in each use is not always easy to discern. The phrase was used from 19c. in a non-pejorative sense "the theory that a (certain) conspiracy exists," especially in court cases. Its use in general reference to theories of hidden cabals pulling wires behind the scenes of national or global events is by 1871.

We shall better understand the ensuing civil war if we study the movements in the four most important of these States, in relation to a theory which asserts that the secession was a conspiracy whose central cabal, composed of Southern senators and representatives in Washington, dictated through its ramifications in the States the inception and the course of the revolution. [James Ford Rhodes, page headed "The Conspiracy Theory" in "History of the United States from the Compromise of 1850," New York, 1893]

To the Jingo Imperialist "the South African Conspiracy" is the alleged Dutch conspiracy to drive the British into the sea. But, to the man accustomed to weigh evidence and to base his opinions on ascertained facts, it is clear that this conspiracy theory is absolutely untenable, for whatever "evidence" has been adduced in support of the theory is nebulous and shadowy in the extreme. ["The South African Conspiracy," in The Westminster Review, January 1902]

"wireless transmission of voice signals with radio waves," 1907, abstracted or shortened from earlier combinations such as radio-receiver (1903), radiophone "instrument for the production of sound by radiant energy" (1881), radio-telegraphy "means of sending telegraph messages by radio rather than by wire" (1898), from radio- as a combining form of Latin radius "beam" (see radius). Use for "radio receiver" is attested by 1913; sense of "sound broadcasting as a medium" also is from 1913.

That winter, however—the winter of 1921-22—[radio] came with a rush. Soon everybody was talking, not about wireless telephony, but about radio. A San Francisco paper described the discovery that millions were making: "There is radio music in the air, every night, everywhere. Anybody can hear it at home on a receiving set, which any boy can put up in an hour." In February President Harding had an outfit installed in his study, and the Dixmoor Golf Club announced that it would install a "telephone" to enable golfers to hear church services. [Frederick Lewis Allen, "Only Yesterday: An Informal History of the 1920's," 1931]

It is not a dream, but a probability that the radio will demolish blocs, cut the strings of red tape, actuate the voice "back home," dismantle politics and entrench the nation's executive in a position of power unlike that within the grasp of any executive in the world's history. [The Reading Eagle, Reading, Pa., U.S.A., March 16, 1924]

As late as July 1921 the New York Times was calling it wireless telephony, and wireless remained widespread until World War II, when military preference for radio established it as the word. As an adjective by 1912, "by radio transmission;" meaning "controlled by radio" is from 1974. Radio _______ as the proper name of a particular radio station or service, "radio station or service from _______" is by 1920. A radio shack (1946) was a small outbuilding housing radio equipment.