'antimonarchist' originates from Greek and modern English combining forms, specifically the prefix 'anti-' from Greek 'antí' meaning 'against', combined with 'monarchist' ultimately from Greek 'monárkhēs' (via Late Latin and Old French), where 'monos' meant 'single' and 'arkhein' meant 'to rule'.

'antimonarchist' was formed in modern English by combining 'anti-' + 'monarchist' (the latter derived from 'monarchy' through Old French and Late Latin). The components 'monos' + 'arkhein' evolved into Latin/Old French forms such as 'monarcha'/'monarque', which entered English as 'monarch' and then produced the agent-form 'monarchist'; the compound with 'anti-' produced 'antimonarchist' in political discourse.

Initially the elements meant 'against' + 'single ruler', and the compound has retained the core sense of 'opposed to monarchy'; over time it has been used both as a descriptor (adjective) and to name individuals or groups (noun) who oppose monarchy.