noun
one given to extremely eccentric or lunatic ideas or actions
a crackpot who wrote threatening letters to public figures
Synonyms: crackbrain, crank, cuckoo, ding-a-ling, harebrain, kook, lunatic, nut, screwball
Related Word: case, character, ||dingbat, eccentric, oddball, oddity, ||wack; loon, loony, madman, maniac