c. 1200, "wild, uninhabited, or uncultivated place," with -ness + Old English wild-deor "wild animal, wild deer;" see wild (adj.) + deer (n.). Similar formation in Dutch wildernis, German Wildernis, though the usual form there is Wildnis.
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).
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.