WordWeb Online

1. Insanely irresponsible
   "an idiotic idea"
   - crackbrained
    
2. Incongruous; inviting ridicule
   "the idiotic excuse that the dog ate his homework"
   - absurd, cockeyed, derisory, laughable, ludicrous, nonsensical, preposterous, ridiculous
    
3. Having a mental age of three to seven years
   - imbecile, imbecilic

See also: daft, dumb, foolish, idiot, idiotically, insane, retarded, stupid

Encyclopedia: Idiotic