WordWeb Online

1. So unreasonable as to invite derision
   "a contribution so small as to be laughable";
   - absurd, cockeyed [informal], derisory, idiotic, ludicrous, nonsensical, preposterous, ridiculous, ridic [informal]
    
2. Arousing or provoking laughter
   "it would have been laughable if it hadn't hurt so much";
   - amusing, comic, comical, funny, mirthful, risible, rib-tickling [informal]

See also: daft [Brit, informal], dumb, foolish, humorous, humourous [Brit, Cdn, non-standard], imbecile, imbecilic, stupid

Encyclopedia: Laughable