'assail' originates from Old French, specifically the word 'assaillir', where the prefix 'a-' (from Latin 'ad-') meant 'to' and the root 'saillir' (from Latin 'salire') meant 'to leap or jump'.

'assail' changed from Old French 'assaillir' and Middle English forms such as 'assailen', and eventually produced the modern English verb 'assail' and the derived noun 'assailer' (plural 'assailers').

Initially it meant 'to leap upon' or 'to rush at', but over time it evolved into its current meaning of 'to attack' (physically or verbally).