WordWeb Online

1. Broadly or extravagantly humorous; resembling farce
   "ludicrous green hair"
   - farcical, ridiculous
    
2. Incongruous; inviting ridicule
   "it is ludicrous to call a cottage a mansion"
   - absurd, cockeyed, derisory, idiotic, laughable, nonsensical, preposterous, ridiculous

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

Encyclopedia: Ludicrous