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.

1570s, "complete suit of armor," from Greek panoplia "complete suit of armor," from pan- "all" (see pan-) + hopla (plural), "arms" of a hoplites ("heavily armed soldier"); see hoplite. Originally in English figurative, of "spiritual armor," etc. (a reference to Ephesians vi); non-armorial sense of "any splendid array" is by 1829. Related: Panoplied.

1660s, "cloth, drapery," from drape (v.). Jive talk slang for "suit of clothes" is attested from 1945. Drapes "curtains" is by 1895. 

in card-playing, "act of trumping when a player has no cards of the suit led," by 1856, from ruff (v.) "trump when unable to follow suit" (1760), from the name of the old game of ruff (1580s), from French roffle, earlier romfle (early 15c.), from Italian ronfa, which is perhaps a corruption of trionfo "triumph" (from French; compare trump (n.1)). The old game, a predecessor of whist, was in vogue c. 1590-1630.