From Middle Dutch wijssegger ‎(“soothsayer”), from Old High German wīzzago, wīzago ‎(“wise man, prophet, soothsayer”), from Proto-Germanic *wītagô ‎(“wise one; prophet”). Cognate with Old English wītega ‎(“wise man, prophet”).

It once meant a learned or wise man, but through 100′s of years of sarcasm, it’s come to mean one who feigns knowledge; one who is wisecracking; an insolent upstart.