imbecile(noun, adjective) adjective1. having a mental age of three to seven yearsSimilar word(s): idiotic, imbecilicSentences with imbecile as an adjective:- hospitals for the imbecile and insane noun1. a person of subnormal intelligenceSimilar word(s): changeling, cretin, idiot, moronDefinition categories: person, simple, simpleton