crackpot(noun, adjective) adjective1. (informal) Eccentric or impractical- a crackpot idea noun1. a whimsically eccentric personSimilar word(s): crank, fruitcake, nut, screwballDefinition categories: person, eccentric, flake, geek, oddballSentences with crackpot as a noun:- Time will tell whether he is a crackpot or a genius for promoting that sort of idea.