late 15c., originally nautical, "to fit with sails," probably from a Scandinavian source (cf. Danish, Norwegian rigge "to equip," Swedish rigga "to rig, harness"), though these may be from English; perhaps ultimately from PIE *reig- "to bind." Slang meaning "to pre-arrange or tamper with results" is attested from 1938, perhaps a different word, from rig (n.) "a trick, swindle, scheme" (1775), earlier "sport, banter, ridicule" (1725), of unknown origin. Also there is rig (v.) "ransack" from 1560s, likewise of unknown origin. Related: Rigged; rigging.