'portent' originates from Latin, specifically the noun 'portentum' (from the verb 'portendere'), where 'por-' (variant of 'pro-') meant 'forth' and 'tendere' meant 'to stretch' (thus implying 'to foretell' or 'to indicate beforehand').

'portent' came into English via Old French 'portent' and Middle English, derived from Latin 'portentum' and the verb 'portendere'; the word moved from Latin into Old French and then into Middle English as the modern English 'portent'.

Initially, it meant 'a sign or warning' (often with supernatural or prophetic connotations); over time it retained that core sense but broadened to include any remarkable or noteworthy sign or event suggesting what may follow.