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.
-ly 2
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.