Etymology
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bile (n.)

"yellow bitter liquid secreted by the liver that aids in digestion," 1660s, from French bile (17c.) "bile," also, informally, "anger," from Latin bilis "fluid secreted by the liver," also in old medicine one of the four humors (also known as choler), thus "bitterness of feeling, peevishness," supposedly caused by excess of bile (especially as black bile, 1797).

The Latin word is of uncertain origin. De Vaan notes apparent cognates for it in British Celtic (Welsh bustl, Middle Cornish bystel, Breton bestl "gall, bile") and writes, "since this word is only found in Italic and Celtic, it is possible that the word is not PIE." But, he adds, if it was borrowed from Celtic into Italic it might be from PIE root *bheid- "to split," which in Germanic has come to meaning "bite," and he notes that "'bile' is a biting substance."

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acid (adj.)

1620s, "of the taste of vinegar," from French acide (16c.) or directly from Latin acidus "sour, sharp, tart" (also figurative, "disagreeable," etc.), adjective of state from acere "to be sour, be sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

Figurative use in English ("sour, sharp, biting") is from 1775; the word was applied to intense colors by 1916; an acid dye (1888) involves an acid bath. Acid rain "highly acidity in rain caused by atmospheric pollution" is recorded by 1859 in reference to England. Acid drop as a kind of hard sugar candy flavored with tartaric acid is by 1835, with drop (n.) in the "lozenge" sense.

Acid test is American English, 1881, in literal use a quick way to distinguish gold from similar metals by application of nitric acid. Fowler wrote (1920) that it was then in vogue in the figurative sense and "became familiar through a conspicuous use of it during the war by President Wilson."

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acid (n.)

1690s, from acid (adj.); originally loosely applied to any substance having a sour taste like vinegar, in modern chemistry it was gradually given more precise definitions from early 18c. and is given to many compounds which do not have such a taste.

The slang meaning "LSD-25" first recorded 1966 (see LSD).

When I was on acid I would see things that looked like beams of light, and I would hear things that sounded an awful lot like car horns. [Mitch Hedberg, 1968-2005, U.S. stand-up comic]

Acid rock (type performed or received by people using LSD) is also from 1966; acid house dance music style is 1988, probably from acid in the hallucinogenic sense + house "dance club DJ music style."

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taurine (n.)

also taurin, chemical substance (aminoethyl-sulphonic acid), 1845, from Latin taurus "bull" (see Taurus) + chemical suffix -ine (2); obtained by German professor Leopold Gmelin in 1826 and so called because it was first found in ox bile.

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biliary (adj.)

"pertaining to bile," 1731, from French biliaire, from bile "bile; peevishness" (see bile). The meaning "bilious in mood or temperament" is recorded from 1837.

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bilirubin (n.)

"reddish pigment found in bile," 1868, from German bilirubin (1864), from bili- "bile" (see bile) + Latin ruber "red" (from PIE root *reudh- "red, ruddy") + -ine (2).

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bilious (adj.)

1540s, "pertaining to bile, biliary," from French bilieux, from Latin biliosus "pertaining to bile," from bilis "bile; peevishness" (see bile). The meaning "testy, peevish, ill-tempered" (as people afflicted with an excess of bile were believed to be) is attested from 1560s. This is the main modern sense in English and French; the more literal meaning being taken up by biliary. Related: Biliousness.

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choler (n.)

late 14c., "bile," as one of the humors, an excess of which was supposed in old medicine to cause irascibility or temper, from Old French colere "bile, anger," from Late Latin cholera "bile" (see cholera).

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cholinergic (adj.)

1934, from choline, name of a basic substance abundant in bile (coined in German, 1862, from Greek khole "bile;" see cholera) + Greek ergon "work" (from PIE root *werg- "to do") + -ic.

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gall (n.1)

"bile, liver secretion," Old English galla (Anglian), gealla (West Saxon) "gall, bile," from Proto-Germanic *gallon "bile" (source also of Old Norse gall "gall, bile; sour drink," Old Saxon galle, Old High German galla, German Galle), from PIE root *ghel- (2) "to shine," with derivatives denoting "green, yellow," and thus "bile, gall." Informal sense of "impudence, boldness" first recorded American English 1882; but meaning "embittered spirit, rancor" is from c. 1200, from the old medicine theory of humors.

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