'agentess' originates from the English word 'agent' with the suffix '-ess' added to denote a female form.

'agent' changed from the Latin word 'agere' meaning 'to do, act' and eventually became the modern English word 'agent'. The suffix '-ess' was added to form 'agentess'.

Initially, 'agent' meant 'one who acts or does', and with the addition of '-ess', it evolved to specifically denote a female agent.