litigious adj.

"act of carrying on a lawsuit," 1640s, from Late Latin litigationem (nominative litigatio), noun of action from past-participle stem of Latin litigare "to dispute, quarrel; sue, go to court," from phrase litem agere "to drive a suit," from litem (nominative lis) "lawsuit, dispute, quarrel, strife" (which is of uncertain origin) + agere "to set in motion, drive forward" (from PIE root *ag- "to drive, draw out or forth, move"). The word was earlier in English in a now obsolete sense "disputation" (1560s). Other legal terms in English from Latin lis included litiscontestation (15c.), litispendence (17c.).

1610s (intransitive), from Latin litigatus, past participle of litigare "to dispute, carry on a suit," from phrase litem agere "to drive a suit," from litem (nominative lis) "lawsuit, dispute, quarrel, strife" (which is of uncertain origin) + agere "to set in motion, drive forward" (from PIE root *ag- "to drive, draw out or forth, move"). Transitive sense is from 1741. Related: Litigated; litigating.