"a passing from one state to another," whether regular or not, 1560s, from Middle French vicissitude (14c.), from Latin vicissitudinem (nominative vicissitudo) "change, interchange, alternation," from vicissim (adv.) "changeably, on the other hand, by turns, in turn," from vicis "a turn, change" (from PIE root *weik- (2) "to bend, to wind"). Related: Vicissitudes.
