1831, "heavyweight horseman," later "boxer or wrestler of a certain weight" (1896), from earlier welter "heavyweight horseman or boxer" (1804), possibly from welt (v.) "beat severely" (c. 1400).
... but at the end of the first German mile, Nature gave way, and this excellent mare was obliged to "knock under" to the extraordinary exertions she had made, and to the welter weight she carried, upwards of 13 stone. [The Sporting Magazine, September 1831]
1590s, "confusion," from welter (v.). The meaning "confused mass" is attested by 1851.
"inspissated juice of the poppy plant," especially as used in medicine from 17c. for relief of pain and production of sleep, late 14c., from Latin opium, from Greek opion "poppy juice, poppy," diminutive of opos "vegetable juice, plant juice, fig curd," from PIE *sokwo- "juice, resin" (source also of Old Church Slavonic soki "juice," Lithuanian sakaī (plural) "resin").
Die Religion ist der Seufzer der bedrängten Kreatur, das Gemüth einer herzlosen Welt, wie sie der Geist geistloser Zustände ist. Sie ist das Opium des Volks. [Karl Marx, "Zur Kritik der Hegel'schen Rechts-Philosophie," in "Deutsch-Französische Jahrbücher," February, 1844]
The British Opium War against China lasted from 1839-42; the name is attested from 1841. Opium-eater, one who habitually uses opium in some form, is by 1821.
Old English wilde "in the natural state, uncultivated, untamed, undomesticated, uncontrolled," from Proto-Germanic *wildia- (source also of Old Saxon wildi, Old Norse villr, Old Frisian wilde, Dutch wild, Old High German wildi, German wild, Gothic wilþeis "wild," German Wild (n.) "game"), of uncertain origin, perhaps from PIE root *welt- "woodlands; wild" (see wold).
Ursula ... hath bin at all the Salsbury rasis, dancing like wild with Mr Clarks. [letter, 1674]
Meaning "sexually dissolute, loose" is attested from mid-13c. Meaning "distracted with excitement or emotion, crazy" is from 1590s. U.S. slang sense of "exciting, excellent" is recorded from 1955. As an adverb from 1540s. Baseball wild pitch is recorded from 1867. Wildest dreams attested from 1717. Wild West in a U.S. context recorded by 1826. Wild Turkey brand of whiskey (Austin Nichols Co.) in use from 1942.