Etymology
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why (adv.)
Old English hwi, instrumental case (indicating for what purpose or by what means) of hwæt (see what), from Proto-Germanic adverb *hwi (source also of Old Saxon hwi, Old Norse hvi), from PIE *kwi- (source of Greek pei "where"), locative of root *kwo-, stem of relative and interrogative pronouns. As an interjection of surprise or emphasis, recorded from 1510s. As a noun, "cause, reason" from c. 1300.
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*kwo- 
also *kwi-, Proto-Indo-European root, stem of relative and interrogative pronouns.

It forms all or part of: cheese (n.2) "a big thing;" cue (n.1) "stage direction;" either; hidalgo; how; kickshaw; neither; neuter; qua; quality; quandary; quantity; quasar; quasi; quasi-; query; quib; quibble; quiddity; quidnunc; quip; quodlibet; quondam; quorum; quote; quotidian; quotient; ubi; ubiquity; what; when; whence; where; whether; which; whither; who; whoever; whom; whose; why.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kah "who, which;" Avestan ko, Hittite kuish "who;" Latin quis/quid "in what respect, to what extent; how, why," qua "where, which way," qui/quae/quod "who, which;" Lithuanian kas "who;" Old Church Slavonic kuto, Russian kto "who;" Old Irish ce, Welsh pwy "who;" Old English hwa, hwæt, hwær, etc.
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how (adv.)
Old English hu "how," from Proto-Germanic *hwo (source also of Old Saxon hwo, Old Frisian, Middle Dutch hu, Dutch hoe, German wie, Gothic hvaiwa "how"), an adverbial form from PIE root *kwo-, stem of relative and interrogative pronouns. Practically a doublet of why, differentiated in form and use.

How come? for "why?" is recorded from 1848 [Bartlett]. Emphatic phrase and how! is recorded from 1865. The formulation was common in book and article titles ("The National Debt, and How to Pay It"), but Pennsylvania writer Bayard Taylor, in whom it is first recorded, seems to have regarded it as a German or German-American expression.
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scalar (adj.)

1650s, "resembling a ladder," from Latin scalaris "of or pertaining to a ladder," from scalae (plural) "ladder, steps, flight of steps" (see scale (n.2)). The noun in the mathematical sense of "a real number" is from 1846, coined by Irish mathematician William R. Hamilton (1805-1865), who can explain why it is the correct word for that.

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leak (n.)
"hole by which liquid enters or escapes," late 15c., from leak (v.) or Old Norse cognate leka. Sense of "revelation of secret information" is from 1950. Meaning "act of urination" is attested from 1934 ("Tropic of Cancer"); but the verb meaning "to piss" is from 1590s: "Why, you will allow vs ne're a Iourden [i.e. a chamberpot], and then we leake in your Chimney." ["I Hen. IV," II.i.22]
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belle (n.)
"beautiful woman well-dressed; reigning beauty," 1620s, from French belle, from Old French bele, from Latin bella, fem. of bellus "beautiful, fair," from PIE *dwenelo-, diminutive form of root *deu- (2) "to do, perform; show favor, revere." "The dim. meaning is the reason why bellus was originally used to refer to women and children; it was applied to men only ironically" [de Vaan].
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maisonette (n.)

1818, "small house," from French maisonnette, diminutive of maison "house" (11c.), from Latin mansionem (see mansion). Meaning "a part of a building let separately" is by 1889.

You see, this is how it stands: I live in what the fellow who let the thing to me called a "maisonette"—goodness only knows why .... [Windsor Magazine, 1902]
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aphid (n.)
1849, Englished from Modern Latin aphides, plural of aphis, coined by Linnaeus (1758), though where he got it and why he applied it to the plant louse are mysteries. The theory favored by OED as "least improbable" is that it derives from the plural of Greek apheides "unsparing, lavishly bestowed," in reference either to the "prodigious rate of production" of the insects or their voracity. The colloquial name was ant-cow (1847). Related: Aphidian (1855).
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turmeric (n.)

pungent powder made from the root of an East Indian plant, 1530s, altered from Middle English turmeryte (early 15c.), which is of uncertain origin. "Middle English Compendium" compares Medieval Latin terra merita (16c.), French terre mérite (17c.), literally "worthy earth," though the reason why it would be called this is obscure. Klein suggests it might be a folk-etymology corruption of Arabic kurkum "curcuma, saffron."

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because (conj.)
late 14c., from phrase bi cause, introducing a subordinate clause or phrase, "by cause, for the reason that," from by (prep.) + cause (n.). Modeled on French par cause. Originally often followed by that or why. As an adverb, "by reason, on account" (with of), from late 14c. Clipped form cause (sometimes 'cause) is attested in writing by mid-15c.
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