n. & adj.
n. 1 a person of abnormally weak intellect, esp. an adult with a mental age of about five. 2 colloq. a stupid person.
adj. mentally weak; stupid, idiotic. imbecilely adv. imbecilic adj. imbecility n. (pl. -ies).
[ F imbécil(l)e f. L imbecillus (as IN-(1), baculum stick) orig. in sense 'without supporting staff' ]