'assassinator' originates from English, specifically formed from the verb 'assassinate' plus the agentive suffix '-ator' (from Latin '-ator'); the element 'assassin' itself ultimately comes from Arabic 'ḥashshāshīn'.

'assassin' entered European languages from Arabic 'ḥashshāshīn' via Medieval Latin and Old French as 'assassin'; the verb 'assassinate' was later formed (from 'assassin' + suffix '-ate'), and 'assassinator' was subsequently formed in English by adding the agentive '-ator'.

Initially the Arabic term referred to the 'ḥashshāshīn' (often interpreted as 'hashish users'); over time the word evolved in European languages to mean 'a killer of a prominent person', and 'assassinator' now specifically denotes 'one who assassinates'.