'antimonarchist' originates from the prefix 'anti-' (from Greek/Modern Latin) meaning 'against', combined with 'monarch' (from Greek 'monárkhēs' where 'mon-' meant 'one' and 'arkhos' meant 'ruler'), plus the agent-forming suffix '-ist'.

'antimonarchist' was formed in English by combining 'anti-' + 'monarch' + '-ist' (a formation typical from the 18th–19th centuries), building on earlier words like 'monarch' and 'monarchist' to denote opposition to monarchy.

Initially it literally meant 'one who is against a monarch or monarchy'; over time the meaning has remained essentially the same and is used to describe political opponents of monarchy or supporters of republicanism.