1540s, "time of merrymaking before Lent," from French carnaval, from Italian carnevale "Shrove Tuesday," from older Italian forms such as Milanese *carnelevale, Old Pisan carnelevare "to remove meat," literally "raising flesh," from Latin caro "flesh" (originally "a piece of flesh," from PIE root *sker- (1) "to cut") + levare "lighten, raise, remove" (from PIE root *legwh- "not heavy, having little weight").
Folk etymology has it from Medieval Latin carne vale " 'flesh, farewell!' " Attested from 1590s in the figurative sense of "feasting or revelry in general." The meaning "a circus or amusement fair" is attested by 1926 in American English.