Synonyms for Idiotic:

adj.

absurd (adjective)
implausible, crazy, silly, inconsistent, senseless, nonsensical, inane, incongruous, absurd, self-contradictory, ridiculous, anachronistic, preposterous, bizarre, irrational, eccentric, outlandish, illogical, foolish, wacky, paradoxical, farcical, fallacious, ludicrous, impossible, meaningless, invalid, loony, tomfool, dippy, contradictory.
asinine (adjective)
half-witted, absurd, cretinous.
balmy (adjective)
dotty.
crazy (adjective)
bizarre, balmy, mad, eccentric, ridiculous.
daft (adjective)
dopey.
demented (adjective)
crackbrained.
dopey (adjective)
slow, thick.
fatuous (adjective)
sappy, brainless, jerky.
foolish (adjective)
goofy, foolish, dim-witted, chuckle-headed, meat-headed, imbecilic, asinine, nitwit, dippy, dotty, inane, tomfool, loony, doltish, lunatic, knuckle-headed, crackpot, blockheaded, dumb, loopy, blithering, moronic, crazy, ignorant, nonsensical, cretinous, dopey, half-witted, absurd, brainless, bone-headed, lame-brained.
idiotic (adjective)
foolish, crazy, harebrained, imbecilic, unintelligent, senseless, thick-witted, inane, moronic, dull, lunatic, fatuous, asinine, insane, silly, dumb.
insane (adjective)
balmy.
lunatic (adjective)
zany.
senseless (adjective)
asinine.
softheaded (adjective)
softheaded.
unintellectual (adjective)
unintelligent, cretinous, moronic, imbecilic, half-wit, unintellectual, defective, foolish.

n.

slow-witted, empty-headed, thick, slow, thick-witted, simple-minded, dull. fatuous. loopy, softheaded, ability, harebrained, wacky, tomfool, mad, zany, balmy, dippy, knowledge, unearthly, jerky, sappy, lunatic. idiotic (noun)
crackbrained, insane.

Other synonyms:

jerky, dippy, empty-headed, simple-minded, loopy, softheaded, fatuous, wacky, slow-witted. harebrained. sappy, zany. dull, unearthly. mad. slow. thick. Other relevant words:
jerky, thick-witted, fatuous, softheaded, crackbrained, sappy, balmy, lunatic, simple-minded, thick, zany, dull, tomfool, mad, empty-headed, insane, wacky, unearthly, harebrained, dippy, slow, slow-witted, loopy.

Usage examples for idiotic

  1. Why had she been such a fool as to count on this poor old idiotic creature? – North, South and Over the Sea by M.E. Francis (Mrs. Francis Blundell)
  2. Idiotic thing to do. – The Way of an Eagle by Ethel M. Dell
  3. At first a great dread filled his heart, only to be followed by a kind of idiotic mirth, over which he had no control. – The Man Who Rose Again by Joseph Hocking