WordNet sense 1 (showing or resulting from lack of judgment or wisdom):

unwise

WordNet sense 2 (very foolish):

harebrained, insane, mad

WordNet sense 3 (absurd or silly because unlikely):

fond

WordNet sense 4 (ludicrous, foolish):

silly, wacky, zany

WordNet sense 5 (devoid of intelligence):

asinine, fatuous, inane

WordNet sense 6 (incongruous;inviting ridicule):

absurd, idiotic, ludicrous, preposterous, ridiculous

WordNet sense 7 (having or revealing stupidity):

dopey, dopy, jerky, anserine, gooselike, goosey, goosy

WordNet sense 8 (lacking or marked by lack of intellectual acuity):

stupid