'imbecile' originates from Latin, specifically the word 'imbecillus', where 'in-' meant 'not' and 'baculum' meant 'staff (a walking stick)', together giving the sense 'without a staff, weak'.

'imbecillus' passed into Middle French and then Modern French as 'imbecile', and the word entered English from French (late Middle English/early Modern English) as 'imbecile'.

Initially, it meant 'weak' or 'feeble' (physical weakness); over time it came to refer to mental weakness and then to the modern insulting sense 'stupid person'.