Etymology
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knock up (v.)

1660s, "arouse by knocking at the door," from knock (v.) + up (adv.). However it is little used in this sense in American English, where the phrase means "get a woman pregnant" (1813), possibly ultimately from knock in a sense "to copulate with" (1590s; compare slang knocking-shop "brothel," 1860).

Knocked up in the United States, amongst females, the phrase is equivalent to being enciente, so that Englishmen often unconsciously commit themselves when amongst our Yankee cousins. [John Camden Hotten, "The Slang Dictionary," London, 1860]
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pick up (v.)

early 14c. as a verbal phrase, "lift and take with the fingers," from pick (v.) + up (adv.). From 1510s as "take or get casually, obtain or procure as opportunity offers." Meaning "take (a person found or overtaken) into a vehicle or vessel," is from 1690s, also, of persons, "make acquaintance or take along" (especially for sexual purposes). Intransitive meaning "improve gradually, reacquire vigor or strength" is by 1741. Sense of "tidy up" is from 1861; that of "arrest" is from 1871; meaning "gain speed" is from 1922; meaning "to pay" (a check, tab, etc.) is from 1945. Pick-me-up "stimulating alcoholic drink" is attested from 1867.

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lucus a non lucendo 

a phrase that stands for "absurd etymology," or generally "anything illogical, outrageous hypothesis," 1711, from the Latin phrase, taken as the outstanding example of such an error.

"A grove (lucus) [is so called] from not (a non) being light" (lucendo, ablative of lucere "to shine;" see light (n.)). That is, it is called a grove because light doesn't get into it. This explanation is found in a commentary on Virgil (Aeneid 1.22) by Servius, a 4th century grammarian, among other places. Other ancient grammarians (notably Quintilian) found it paradoxical and absurd, based on nothing more than the similarity in sound between the two words.

Modern scholarship, however, concludes that lucus and lucere probably do come both from the same PIE root (*leuk-) meaning "light, bright." De Vaan writes: "Lucus 'sacred grove, wood,' from PIE *louk-o- 'light place,' with cognates in Sanskrit loka- 'free space, world,' Lithuanian laukas 'field, land,' Latvian lauks 'field, clearing in the woods,' Old High German loh 'clearing' and English lea 'open field, meadow, piece of untilled grassy ground.' " Apparently the primeval notion in *louk-o- was a lighter place in a thick forest. Migration, change of climate, or felling of the woods might have shifted the meaning.

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hat trick (n.)

in the sports sense, 1879, originally in cricket, "taking three wickets on three consecutive deliveries;" extended to other sports c. 1909, especially ice hockey ("In an earlier contest we had handed Army a 6-2 defeat at West Point as Billy Sloane performed hockey's spectacular 'hat trick' by scoring three goals" ["Princeton Alumni Weekly," Feb. 10, 1941]). So called allegedly because it entitled the bowler to receive a hat from his club commemorating the feat (or entitled him to pass the hat for a cash collection), but the term probably has been influenced by the image of a conjurer pulling objects from his hat (an act attested by 1876). The term was used earlier for a different sort of magic trick:

Place a glass of liquor on the table, put a hat over it, and say, "I will engage to drink every drop of that liquor, and yet I'll not touch the hat." You then get under the table; and after giving three knocks, you make a noise with your mouth, as if you were swallowing the liquor. Then, getting from under the table, say "Now, gentlemen, be pleased to look." Some one, eager to see if you have drunk the liquor, will raise the hat; when you instantly take the glass and swallow the contents, saying, "Gentlemen I have fulfilled my promise: you are all witnesses that I did not touch the hat." ["Wit and Wisdom," London, 1860]
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