litigant n.

"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.).