Origin and history of wonky

late 13c., wenche, "girl, young woman," especially if unmarried, also "female infant;" shortened from wenchel "child," also in early Middle English "girl, maiden," from Old English wencel, which is probably related to wancol "unsteady, fickle, weak," from Proto-Germanic *wankila- (source also of Old Norse vakr "child, weak person," Old High German wanchal "fickle"), from PIE *weng- "to bend, curve" (see wink (v.)).

The wenche is nat dead, but slepith. [Wycliffe, Matthew ix.24, c. 1380]

In Shakespeare's day a female flax-worker could be a flax-wench, flax-wife, or flax-woman. In Middle English occasionally with disparaging suggestion, indicated by context, "lewd or indiscrete woman," and a secondary sense of "concubine, strumpet" is attested by mid-14c. Also "serving-maid, bondwoman, young woman of a humble class" (late 14c.), a sense retained colloquially in the 19c. U.S. South in reference to slave women of any age.

"overly studious person," 1962, earlier "effeminate male" (1954), American English student slang. Perhaps a shortening of British slang wonky "shaky, unreliable," or a variant of British slang wanker "masturbator."

It seems to have risen from Ivy League slang into currency late 1980s as a synonym for nerd, and as such was popularized 1993 during the presidency of Bill Clinton. Tom Wolfe (1988) described it as "an Eastern prep-school term referring to all those who do not have the 'honk' voice, i.e., all who are non-aristocratic."