'assemblyman' originates from English, specifically formed from the noun 'assembly' + the noun 'man'. 'assembly' comes from Old French 'assemblée' meaning 'a gathering' (from the verb 'assembler' 'to bring together'), and 'man' comes from Old English 'mann' meaning 'person, human'.

'assemblyman' developed in Modern English by compounding the existing English words 'assembly' and 'man' (Middle English and Early Modern English periods) and came to be used to refer to a member of a legislative assembly.

Initially, it specifically meant 'a male member of an assembly', but over time usage has shifted toward gender-neutral senses in many contexts (often replaced by 'assembly member'); nevertheless 'assemblyman' is still used in some places and contexts to mean 'member of an assembly'.