Same word as kneeslapper:

absurd, amusing, antic, blithe, capricious, clever, diverting, droll, entertaining, facetious, farcical, for grins, gas, gay, gelastic, good-humored, hilarious, humdinger, hysterical, jocose, jocular, joking, jolly, killing, knee-slapper, laughable, ludicrous, merry, mirthful