1560s, "disputation," from L.L. litigationem (nom. litigatio), from L. litigatus, pp. of litigare "to dispute, quarrel, strive," from litem (nom. lis, gen. litis) "lawsuit, dispute, quarrel, strife" + root of agere "to drive, conduct" (see act
). Meaning "act of carrying on a lawsuit" is from 1640s.