Etymology
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Mach 
measure of speed relative to the speed of sound (technically Mach number), 1937, named in honor of Austrian physicist Ernst Mach (1838-1916).
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Angstrom (n.)
unit of length equal to one hundred millionth of a centimeter (used to measure wavelengths of light), 1892, named for Swedish physicist Anders Ångström (1814-1874).
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Spenserian (adj.)
1817, from Edmund Spenser (c. 1552-1599), Elizabethan poet (for the origin of the surname, see Spencer). Spenserian stanza, which he employed in the "Faerie Queen," consists of eight decasyllabic lines and a final Alexandrine, with rhyme scheme ab ab bc bcc.

"The measure soon ceases to be Spenser's except in its mere anatomy of rhyme-arrangement" [Elton, "Survey of English Literature 1770-1880," 1920]; it is the meter in Butler's "Hudibras," Scott's "Lady of the Lake," and notably the "Childe Harold" of Byron, who found (quoting Beattie) that it allowed him to be "either droll or pathetic, descriptive or sentimental, tender or satirical, as the humour strikes me; for, if I mistake not, the measure which I have adopted admits equally of all these kinds of composition."
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Arian (adj.)

late 14c., Arrian, "adhering to the doctrines of Arius," from Late Latin Arianus, "pertaining to the doctrines of Arius," priest in Alexandria early 4c., who posed the question of Christ's nature in terms which appeared to debase the Savior's relation to God (denial of consubstantiation). Besides taking an abstract view of Christ's nature, he reaffirmed man's capacity for perfection. The doctrines were condemned at Nice, 325, but the dissension was widespread and split the Church for about a century during the crucial time of barbarian conversions. The name is Greek, literally "warlike, of Ares."

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Dionysian (adj.)

c. 1600, of or pertaining to Dionysos (Latin Dionysus), Greek god of wine and revelry, identified with Roman Bacchus. His name is of unknown origin. In some cases a reference to historical men named Dionysius, such as the two tyrants of that name of Syracuse, both notorious for cruelty, or Dionysius Exiguus, 6th c. Scythian monk who invented the Anno Domini era (see A.D.). The reference is to him in Dionysian period, a measure of 532 Julian years, at the end of which the full moons recur on the same days of the year.

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Peter Pan (n.)

name of the boy-hero in J.M. Barrie's play "Peter Pan, or The Boy Who Wouldn't Grow Up" (1904), first introduced in Barrie's "The Little White Bird" (1902). Used allusively for an immature adult man from 1914 (by G.B. Shaw, in reference to the Kaiser).

Well, Peter Pan got out by the window, which had no bars. Standing on the ledge he could see trees far away, which were doubtless the Kensington Gardens, and the moment he saw them he entirely forgot that he was now a little boy in a nightgown, and away he flew, right over the houses to the Gardens. It is wonderful that he could fly without wings, but the place itched tremendously, and, perhaps we could all fly if we were as dead-confident-sure of our capacity to do it as was bold Peter Pan that evening. [Barrie, "The Little White Bird"]
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K 

eleventh Roman letter, from Greek kappa, from Phoenician kaph or a similar Semitic source, said to mean literally "hollow of the hand" and to be so called for its shape.

Little used in classical Latin, which at an early age conformed most of its words (the exceptions had ritual importance) to a spelling using -c- (a character derived from Greek gamma). In Late Latin, pronunciation of -c- shifted (in the direction of "s"). Greek names brought into Latin also were regularized with a -c- spelling, and then underwent the Late Latin sound-shift; hence the modern pronunciation of Cyrus, Circe. To keep their pronunciation clear, the many Greek words (often Church words) that entered Latin after this shift tended to take Latin -k- for Greek kappa.

K- thus became a supplementary letter to -c- in Medieval Latin, used with Greek and foreign words. But most of the languages descended from Latin had little need of it, having evolved other solutions to the sound shifts.

K- also was scarce in Old English. After the Norman conquest, new scribal habits restricted -c- and expanded the use of -k-, which began to be common in English spelling from 13c. This probably was done because the sound value of -c- was evolving in French and the other letter was available to clearly mark the "k" sound for scribes working in English. For more, see C.

In words transliterated from Arabic, Hebrew, Turkish, Japanese, Hawaiian, etc., it represents several different sounds lumped. In modern use some of them are now with kh-; in older borrowings they often followed traditional English spelling and were written with a C- (Corea, Caaba, etc.).

As a symbol for potassium, it represents Latin kalium "potash." In CMYK as a color system for commercial printing it means "black" but seems to stand for key in a specialized printing sense. Slang meaning "one thousand dollars" is 1970s, from kilo-. K as a measure of capacity (especially in computer memory) meaning "one thousand" also is an abbreviation of kilo-.

As an indication of "strikeout" in baseball score-keeping it dates from 1874 and is said to represent the last letter of struck. The invention of the scorecard symbols is attributed to English-born U.S. newspaperman Henry Chadwick (1824-1908) principally of the old New York "Clipper," who had been writing baseball since 1858, and who explained it thus:

Smith was the first striker, and went out on three strikes, which is recorded by the figure "1" for the first out, and the letter K to indicate how put out, K being the last letter of the word "struck." The letter K is used in this instance as being easier to remember in connection with the word struck than S, the first letter, would be. [Henry Chadwick, "Chadwick's Base Ball Manual," London, 1874]
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Peoria 

small city in Illinois, U.S., originally the name of a subdivision of the Miami/Illinois people (1673), from native /peewaareewa/. Their own name is said to mean "carriers." The place name also is found in Oklahoma and Iowa, but it is the Illinois city that has been proverbially regarded as the typical measure of U.S. cultural and intellectual standards at least since Ambrose Bierce (c. 1890). Also the butt of baseball player jokes (c. 1920-40, when a team there was part of the St. Louis Cardinals farm system) and popularized in the catchphrase It'll play in Peoria (often negative), meaning "the average American will approve," which was popular in the Nixon White House (1969-74) but seems to have had a vaudeville origin. Personification in little old lady in Peoria is said to be from Harold Ross of the New Yorker. Peoria's rivals as embodiment of U.S. small city values and standards include Dubuque, Iowa; Hoboken and Hackensack, N.J.; Oakland (Gertrude Stein: "When you get there, there isn't any there there") and Burbank, Calif., and the entire state of North Dakota.

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Gradgrind (n.)

"cold, factual person," from the name of the school-board superintendent and mill-owner in Dickens' "Hard Times" (1854):

THOMAS GRADGRIND, sir. A man of realities. A man of facts and calculations. A man who proceeds upon the principle that two and two are four, and nothing over, and who is not to be talked into allowing for anything over. Thomas Gradgrind, sir - peremptorily Thomas - Thomas Gradgrind. With a rule and a pair of scales, and the multiplication table always in his pocket, sir, ready to weigh and measure any parcel of human nature, and tell you exactly what it comes to. It is a mere question of figures, a case of simple arithmetic. ....
In such terms Mr. Gradgrind always mentally introduced himself, whether to his private circle of acquaintance, or to the public in general. In such terms, no doubt, substituting the words 'boys and girls,' for 'sir,' Thomas Gradgrind now presented Thomas Gradgrind to the little pitchers before him, who were to be filled so full of facts.
Indeed, as he eagerly sparkled at them from the cellarage before mentioned, he seemed a kind of cannon loaded to the muzzle with facts, and prepared to blow them clean out of the regions of childhood at one discharge. He seemed a galvanizing apparatus, too, charged with a grim mechanical substitute for the tender young imaginations that were to be stormed away. 
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Valentine (n.)

mid-15c., "sweetheart chosen on St. Valentine's Day," from Late Latin Valentinus, the name of two early Italian saints (from Latin valentia "strength, capacity;" see valence). Choosing a sweetheart on this day originated 14c. as a custom in English and French court circles. Meaning "letter or card sent to a sweetheart" first recorded 1824. The romantic association of the day is said to be from it being around the time when birds choose their mates.

For this was on seynt Volantynys day
Whan euery bryd cometh there to chese his make.
[Chaucer, "Parlement of Foules," c. 1381]

Probably the date was the informal first day of spring in whatever French region invented the custom (many surviving medieval calendars reckon the start of spring on the 7th or 22nd of February). No evidence connects it with the Roman Lupercalia (an 18c. theory) or to any romantic or avian quality in either of the saints. The custom of sending special cards or letters on this date flourished in England c. 1840-1870, declined around the turn of the 20th century, and revived 1920s.

To speak of the particular Customs of the English Britons, I shall begin with Valentine's Day, Feb. 14. when young Men and Maidens get their several Names writ down upon Scrolls of Paper rolled up, and lay 'em asunder, the Men drawing the Maidens Names, and these the Mens; upon which, the Men salute their chosen Valentines and present them with Gloves, &c. This Custom (which sometimes introduces a Match) is grounded upon the Instinct of Animals, which about this Time of the Year, feeling a new Heat by the approach of the Sun, begin to couple. ["The Present State of Great Britain and Ireland" London, 1723]
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