The Collaborative International Dictionary of English v.0.48:

humourous \humourous\ adj.
   same as humorous; causing amusement or laughter. [Narrower
   terms: bantering, facetious, tongue-in-cheek, witty ;
   {boisterous, knockabout, slapstick ; {buffoonish, clownish,
   zany; comic, comical, funny, laughable, risible ; {droll,
   waggish ; {dry, ironic, ironical, pawky, wry ; {farcical,
   ludicrous, ridiculous ; {Gilbertian ; {hilarious, uproarious
   ; {jesting, jocose, jocular, jocund, joking; merry,
   mirthful; seriocomic, seriocomical ; {tragicomic,
   tragicomical ; {killing, sidesplitting] Also See:
   pleasing.

   Syn: humorous.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

humourous
    adj 1: full of or characterized by humor; "humorous stories";
           "humorous cartoons"; "in a humorous vein" [syn:
           humorous, humourous] [ant: humorless, humourless,
           unhumorous]