'causer' originates from the English verb 'cause', ultimately from Latin, specifically the word 'causa', where 'causa' meant 'reason' or 'cause'.

'causa' in Latin passed into Old French as 'cause/causer', entered Middle English as 'causen'/'cause', and the agent-form '-er' produced the English noun 'causer'.

Initially related to the idea of a 'reason' or 'legal cause' in Latin, it evolved into the English verb 'to cause' and then into the agent noun 'causer' meaning 'one that causes'.