1540s, "time of merrymaking before Lent," from French carnaval, from Italian carnevale "Shrove Tuesday," from older Italian forms such as Milanese *carnelevale, Old Pisancarnelevare "to remove meat," literally "raising flesh," from Latin caro "flesh" (see carnage) + levare "lighten, raise, remove" (see lever (n.)). Folk etymology is from Medieval Latin carne vale " 'flesh, farewell!' " Meaning "a circus or fair" is attested by 1931 in North America.
reference：http://www.etymonline.com/index.php?allowed_in_frame=0&search=carnival&searchmode=none