Synonyms for Crackpot:

adj.

foolish (adjective)
dotty, blockheaded, dim-witted, brainless, goofy, bone-headed, loony, chuckle-headed, doltish, imbecilic, ignorant, foolish, absurd, dumb, moronic, idiotic, dopey, blithering, half-witted, knuckle-headed, asinine, nonsensical, inane, cretinous, lame-brained, crazy, nitwit, meat-headed.
lunatic (adjective)
nutty, neurotic, crazy, psychotic, lunatic, kooky, mad, Fiendish.

n.

ludicrous, cuckoo, not in your right mind/not right in the head, laughable, eccentric, ding-a-ling, dingbat, weirdo, wise, childish, ridiculous, weirdie, over-the-top. crackpot (noun)
fruitcake, nut, crank, nutcase, screwball, nut case.
eccentric (noun)
kook, lunatic, crank, nut, screwball, maniac.
eccentric person (noun)
kook.
fool (noun)
moron, bonehead, dimwit, nincompoop, imbecile, cretin, lame-brain, ignoramus, dolt, clod, fool, half-wit, bungler, knuckle-head, simpleton, blockhead, meathead, loon, chuckle-head, dummy, dunce, dullard, dumbbell.
lunatic (noun)
psychopath, kook, crank, madman, maniac, fiend, nut.
person (noun)
crank, nut case, fruitcake, screwball, nut.

Other synonyms:

cuckoo, dingbat, weirdie, ding-a-ling, weirdo. Other relevant words:
eccentric, cuckoo, nut case, wise, weirdo, screwball, childish, ludicrous, ding-a-ling, fruitcake, weirdie, ridiculous, over-the-top, nutcase, dingbat, laughable.

Usage examples for crackpot

  1. At Garlock's request, all sixteen members of the " crackpot group- the most active members of the Deep Space Club- had been invited to the banquet. – The Galaxy Primes by Edward Elmer Smith
  2. No one wrapped up in massive fuel consumption, tons of lift and such is going to have time to worry about a crackpot who thinks he has found a minor slip in Newton's laws. – Toy Shop by Henry Maxwell Dempsey