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."
"small citrus fruit, a cross between a tangerine and a sour orange," 1926, from French clémentine (1902). Originally an accidental hybrid said to have been cultivated from c. 1900 by (and named for) Father Clement Rodier in the garden of his orphanage in Misserghin, near Oran, Algeria. Introduced into U.S. and grown at Citrus Research Center in Riverside, California, as early as 1909.
curd of milk coagulated, separated from the whey, pressed and used as food, Old English cyse (West Saxon), cese (Anglian) "cheese," from West Germanic *kasjus (source also of Old Saxon kasi, Old High German chasi, German Käse, Middle Dutch case, Dutch kaas), from Latin caseus "cheese" (source of Italian cacio, Spanish queso, Irish caise, Welsh caws).
Of unknown origin; perhaps from a PIE root *kwat- "to ferment, become sour" (source also of Prakrit chasi "buttermilk;" Old Church Slavonic kvasu "leaven; fermented drink," kyselu "sour," -kyseti "to turn sour;" Czech kysati "to turn sour, rot;" Sanskrit kvathati "boils, seethes;" Gothic hwaþjan "foam").
But de Vaan writes, "no etymology can be found which does not require some poorly-founded assumptions," and suggests a loan-word. Also compare fromage. Old Norse ostr, Danish ost, Swedish ost are related to Latin ius "broth, sauce, juice."
Earliest references would be to compressed curds of milk used as food; pressed or molded cheeses with rinds are from 14c. Transferred to other cheese-like substances by 1530s. As a photographer's word to make subjects hold a smile, it is attested from 1930, but in a reminiscence of schoolboy days, which suggests an earlier use. Probably for the forced smile involved in making the -ee- sound.
Green cheese is that newly made; the notion that the moon is made of green cheese as a type of a ridiculous assertion is from 1520s. To make cheeses (1835) was a schoolgirls' amusement of wheeling rapidly so one's petticoats blew out in a circle then dropping down so they came to rest inflated and resembling a wheel of cheese; hence, used figuratively for "a deep curtsy." Bartlett ("Dictionary of Americanisms," 1848) defines head cheese as "The ears and feet of swine cut up fine, and, after being boiled, pressed into the form of a cheese."
c. 1200, asprete "hardship," from Old French asperité "difficulty, painful situation, harsh treatment" (12c., Modern French âpreté), a figurative use, from Latin asperitatem (nominative asperitas) "roughness," from asper "rough, harsh," which is of unknown origin. The Latin adjective was used also of sour wine, bad weather, and hard times. The figurative meaning "harshness of feeling" in English is attested from 1660s; the literal sense of "roughness of surface" is from early 15c.
originally of texture, "hairy," 1530s, probably from Middle English harske "rough, coarse, sour" (c. 1300), a northern word of Scandinavian origin (compare Danish and Norwegian harsk "rancid, rank"), related to Middle Low German harsch "rough, raw," German harst "a rake;" perhaps from PIE root *kars- "to scrape, scratch, rub, card" (source also of Lithuanian karšiu, karšti "to comb," Old Church Slavonic krasta, Russian korosta "scab," Latin carduus "thistle," Sanskrit kasati "rubs, scratches"). Meaning "offensive to feelings" is from 1570s; that of "disagreeable, rude" from 1610s.
c. 1600, "of nitre, pertaining to nitre," from Latin nitrosus, from nitrum (see nitre). The more precise use in chemistry (designating a compound in which the nitrogen has a lower valence than the corresponding nitric compound) is from 1780s. Middle English had nitrose "nitrous in quality; bitter, sour" (early 15c.). Nitrous oxide "laughing gas" is attested from 1800.
When inhaled it produces unconsciousness and insensibility to pain; hence it is used as an anesthetic during short surgical operations. When it is breathed diluted with air an exhilarating or intoxicating effect is produced under the influence of which the inhaler is irresistibly impelled to do all kinds of silly and extravagant acts; hence the old name of laughing-gas. [Century Dictionary, 1895]