1540s, from Latin, literally "let him beware," 3rd person singular present subjunctive of cavere "to beware, take heed, watch, guard against," from PIE root *skeue- "to pay attention, perceive" (cognates: Sanskrit kavih "wise, sage, seer, poet;" Lithuanian kavoti "tend, safeguard;" Armenian cucanem "I show;" Latin cautio "wariness;" Greek koein "to mark, perceive, hear," kydos "glory, fame," literally "that which is heard of;" Old Church Slavonic chujo "to feel, perceive, hear," cudo "wonder," literally "that which is heard of;" Czech (z)koumati "to perceive, be aware of;" Serbian chuvati "watch, heed;" Old English sceawian "to look at" (source of show, v.); Middle Dutch schoon "beautiful, bright," properly "showy;" Gothic hausjan "hear").