peabrain /ˈpiːbɹeɪn/noun 2adjective 1forms 3 noun2 •(informal, offensive) A stupid or clumsy person; a cretin. •(informal, offensive) The brain of such a person.Bungo would gladly have put a bullet in Mr. King's little pea brain. — 1986 adjective1 •(informal, offensive) Stupid, clumsy, idiot formspeabrains · more peabrain · most peabrain