Old English to "in the direction of, for the purpose of, furthermore," from West Germanic *to (source also of Old Saxon and Old Frisian to, Dutch toe, Old High German zuo, German zu "to"), from PIE pronominal base *do- "to, toward, upward" (source also of Latin donec "as long as," Old Church Slavonic do "as far as, to," Greek suffix -de "to, toward," Old Irish do, Lithuanian da-), from demonstrative *de-. Not found in Scandinavian, where the equivalent of till (prep.) is used.
The nearly universal use of to with infinitives (to sleep, to dream, etc.) arose in Middle English out of the Old English dative use of to, and it helped drive out the Old English inflectional endings (though in this use to itself is a mere sign, without meaning).
Commonly used as a prefix in Middle English (to-hear "listen to," etc.), but few of these survive (to-do, together, and time references such as today, tonight, tomorrow — Chaucer also has to-yeere). To and fro "side to side" is attested from mid-14c. Phrase what's it to you "how does that concern you?" (1819) is a modern form of an old question:
Huæd is ðec ðæs?
[John xxi:22, in Lindisfarne Gospel, c.950]
1550s, "one of the ancient sect of philosophy founded by Antisthenes," from Latinized form of Greek kynikos "a follower of Antisthenes," literally "dog-like," from kyōn (genitive kynos) "dog" (from PIE root *kwon- "dog").
Supposedly the name is a reference to the coarseness of life and sneering surliness of the philosophers, and the popular association even in ancient times was "dog-like" (Lucian has kyniskos "a little cynic," literally "puppy").
But more likely it is from Kynosarge "The Gray Dog," the name of the gymnasium outside ancient Athens (for the use of those who were not pure Athenians) where Antisthenes (a pupil of Socrates), taught. Diogenes was the most famous. Meaning "sneering sarcastic person" is from 1590s. As an adjective from 1630s.
[Diogenes] studied philosophy under Antisthenes, a crusty type who hated students, emphasized self-knowledge, discipline, and restraint, and held forth at a gymnasium named The Silver Hound in the old garden district outside the city. It was open to foreigners and the lower classes, and thus to Diogenes. Wits of the time made a joke of its name, calling its members stray dogs, hence cynic (doglike), a label that Diogenes made into literal fact, living with a pack of stray dogs, homeless except for a tub in which he slept. He was the Athenian Thoreau. [Guy Davenport, "Seven Greeks"]
Old English hætu, hæto "heat, warmth, quality of being hot; fervor, ardor," from Proto-Germanic *haita- "heat" (source also of Old Saxon hittia, Old Norse hiti, Old Frisian hete, German hitze "heat," Gothic heito "fever"), from the same source as Old English hat "hot" and hæða "hot weather" (see hot).
Meaning "a single course in a race," especially a horse race, is from 1660s, perhaps from earlier figurative sense of "violent action; a single intense effort" (late 14c.), or the meaning "run given to a horse to prepare for a race" (1570s). The latter word over time was extended to "division of a race or contest when there are too many contestants to run at once," the winners of each heat then competing in a final race.
Meaning "sexual excitement in animals" is from 1768, especially of females, corresponding to rut in males. Meaning "trouble with the police" attested by 1920. Heat wave "period of excessive hot weather" first attested 1890; earlier in reference to solar cycles. Heat-stroke is from 1858. Heat-seeking (adj.) of missiles, etc., is by 1955. Red heat, white heat are in reference to the color of heated metals, especially iron.
c. 1200, flour, also flur, flor, floer, floyer, flowre, "the blossom of a plant; a flowering plant," from Old French flor "flower, blossom; heyday, prime; fine flour; elite; innocence, virginity" (12c., Modern French fleur), from Latin florem (nominative flos) "flower" (source of Italian fiore, Spanish flor), from PIE root *bhel- (3) "to thrive, bloom."
From late 14c. in English as "blossoming time," also, figuratively, "prime of life, height of one's glory or prosperity, state of anything that may be likened to the flowering state of a plant." As "the best, the most excellent; the best of its class or kind; embodiment of an ideal," early 13c. (of persons, mid-13c. of things); for example flour of milk "cream" (early 14c.); especially "wheat meal after bran and other coarse elements have been removed, the best part of wheat" (mid-13c.). Modern spelling and full differentiation from flour (n.) is from late 14c.
In the "blossom of a plant" sense it ousted its Old English cognate blostm (see blossom (n.)). Also used from Middle English as a symbol of transitoriness (early 14c.); "a beautiful woman" (c. 1300); "virginity" (early 14c.). Flower-box is from 1818. Flower-arrangement is from 1873. Flower child "gentle hippie" is from 1967.
c. 1300, distaunce, "a dispute or controversy, civil strife, rebellion;" early 14c., "disagreement, discord, strife;" from Old French destance "discord, quarrel" (13c.), with later senses directly from Latin distantia "a standing apart," from distantem (nominative distans) "standing apart, separate, distant," present participle of distare "stand apart," from dis- "apart, off" (see dis-) + stare "to stand," from PIE root *sta- "to stand, make or be firm."
Meaning "remoteness of space, extent of space between two objects or places" is from late 14c. Also "an interval of time" (late 14c., originally distaunce of times). Meaning "remote part of a field of vision" is by 1813. The figurative sense of "aloofness, remoteness in personal intercourse" (1590s) is the same as in stand-offish.
At a distance "far away" is from 1650s. To keep (one's) distance was originally figurative (c. 1600). Phrase go the distance (1930s) seems to be originally from the prize ring, where the word meant "scheduled length of a bout." But it also was a term in 19c. horse-racing heats, where distance meant "the space behind the winning horse in a race that other competing horses must be inside to avoid being disqualified for subsequent heats."
I would hate to see some old railroad man come here and take my job, and then, I don't think it is right to hire some Hill Billy and give him the same right as I just because he was hired the same time I was. [The Railroad Trainmen's Journal, vol. ix, July 1892]
In short, a Hill-Billie is a free and untrammelled white citizen of Alabama, who lives in the hills, has no means to speak of, dresses as he can, talks as he pleases, drinks whiskey when he gets it, and fires of his revolver as the fancy takes him. [New York Journal, April 23, 1900]
In Scott's collection of Border ballads, billie is a frequent term of address or intimacy, "comrade, companion, a brother in arms," "a term expressive of affection and familiarity" also "a brother; a wooer of a woman," and generally "a young man" [Jamieson, 2nd edition]. It is said to be a variant of bully (n.) in its old sense of "sweetheart," also "fine fellow."
1530s (in Anglo-Latin from mid-13c.), via medieval French and Italian Assissini, Assassini, from Arabic hashīshīn (12c.), an Arabic nickname, variously explained, for the Nizari Ismaili sect in the Middle East during the Crusades, plural of hashishiyy, from the source of hashish (q.v.).
They were a fanatical Muslim sect in the mountains of Lebanon at the time of the Crusades, under leadership of the "Old Man of the Mountains" (which translates Arabic shaik-al-jibal, name applied to Hasan ibu-al-Sabbah). In Western European minds 12c.-13c. they had a reputation for murdering opposing leaders after intoxicating themselves by eating hashish, but there is no evidence that the medieval Ismailis used hashish.
The plural suffix -in was mistaken in Europe for part of the word (compare Bedouin). Middle English had the word as hassais (mid-14c.), from Old French hassasis, assasis, which is from the Arabic word.
The generalization of the sect's nickname to the meaning of any sort of assassin happened in Italian at the start of the 14th century. The word with the generalized meaning was often used in Italian in the 14th and 15th centuries. In the mid 16th century the generalized Italian word entered French, followed a little later by English. ["English Words of Arabic Ancestry"]
"a featherless plantigrade biped mammal of the genus Homo" [Century Dictionary], Old English man, mann "human being, person (male or female); brave man, hero;" also "servant, vassal, adult male considered as under the control of another person," from Proto-Germanic *mann- (source also of Old Saxon, Swedish, Dutch, Old High German man, Old Frisian mon, German Mann, Old Norse maðr, Danish mand, Gothic manna "man"), from PIE root *man- (1) "man." For the plural, see men.
Sometimes connected to root *men- (1) "to think," which would make the ground sense of man "one who has intelligence," but not all linguists accept this. Liberman, for instance, writes, "Most probably man 'human being' is a secularized divine name" from Mannus [Tacitus, "Germania," chap. 2], "believed to be the progenitor of the human race."
Specific sense of "adult male of the human race" (distinguished from a woman or boy) is by late Old English (c. 1000); Old English used wer and wif to distinguish the sexes, but wer began to disappear late 13c. and was replaced by man. Universal sense of the word remains in mankind and manslaughter. Similarly, Latin had homo "human being" and vir "adult male human being," but they merged in Vulgar Latin, with homo extended to both senses. A like evolution took place in Slavic languages, and in some of them the word has narrowed to mean "husband." PIE had two other "man" roots: *uiHro "freeman" (source of Sanskrit vira-, Lithuanian vyras, Latin vir, Old Irish fer, Gothic wair; see *wi-ro-) and *hner "man," a title more of honor than *uiHro (source of Sanskrit nar-, Armenian ayr, Welsh ner, Greek anēr; see *ner- (2)).
Man also was in Old English as an indefinite pronoun, "one, people, they." It was used generically for "the human race, mankind" by c. 1200. As a word of familiar address, originally often implying impatience, c.1400; hence probably its use as an interjection of surprise or emphasis, since Middle English but especially popular from early 20c.
As "a woman's lover," by mid-14c. As "adult male possessing manly qualities in an eminent degree," from 14c. Man's man, one whose qualities are appreciated by other men, is by 1873. Colloquial use of the Man for "the boss" is by 1918. To be man or mouse "be brave or be timid" is from 1540s. Meaning "piece with which a game (especially chess) is played" is from c. 1400.
Man-about-town "man of the leisure class who frequents clubs, theaters, and other social resorts" is from 1734. Man of the world is from mid-14c. as "secular man, layman;" by early 15c. as "man experienced in the ways of the world, one able to take things in stride." To do something as one man "unanimously" is from late 14c.
So I am as he that seythe, 'Come hyddr John, my man.' 
MANTRAP, a woman's commodity. [Grose, "Dictionary of the Vulgar Tongue," London, 1785]
At the kinges court, my brother, Ech man for himself. [Chaucer, "Knight's Tale," c. 1386]
late 14c., "lucky, favored by fortune, being in advantageous circumstances, prosperous;" of events, "turning out well," from hap (n.) "chance, fortune" + -y (2). Sense of "very glad" first recorded late 14c. Meaning "greatly pleased and content" is from 1520s. Old English had eadig (from ead "wealth, riches") and gesælig, which has become silly. Old English bliðe "happy" survives as blithe. From Greek to Irish, a great majority of the European words for "happy" at first meant "lucky." An exception is Welsh, where the word used first meant "wise."
Happy medium "the golden mean" is from 1702. Happy ending in the literary sense recorded from 1756. Happy as a clam (1630s) was originally happy as a clam in the mud at high tide, when it can't be dug up and eaten. Happy hunting ground, the reputed Native American paradise, is attested from 1840, American English. Happy day for "wedding day" is by 1739; happy hour for "early evening period of discount drinks and free hors-d'oeuvres at a bar" is by 1961, said to be 1950s. Rock-happy (1945) was U.S. Pacific theater armed forces slang for "mentally unhinged after too much time on one island." Related: Happier; happiest.
Happy family an assemblage of animals of diverse habits and propensities living amicably, or at least quietly, together in one cage. [Century Dictionary]
Middle English folwen, from Old English folgian, fylgian, fylgan "to accompany (especially as a disciple), move in the same direction as; follow after, pursue, move behind in the same direction," also "obey (a rule or law), conform to, act in accordance with; apply oneself to (a practice, trade, or calling)," from Proto-Germanic *fulgojanan (source also of Old Saxon folgon, Old Frisian folgia, Middle Dutch volghen, Dutch volgen, Old High German folgen, German folgen, Old Norse fylgja "to follow"). Probably originally a compound, *full-gan, with a sense of "full-going," the sense then shifting to "serve, go with as an attendant" (compare fulfill). Related: Followed; following.
Sense of "accept as leader or guide, obey or be subservient to" was in late Old English. Meaning "come after in time" is from c. 1200; meaning "to result from" (as effect from cause) is from c. 1200. Meaning "to keep up with mentally, comprehend" is from 1690s. Intransitive sense "come or go behind" is from mid-13c. To follow one's nose "go straight on" first attested 1590s. "The full phrase is, 'Follow your nose, and you are sure to go straight.' " [Farmer]. The children's game follow my leader is attested by that name from 1812 (as follow the leader by 1896).