'antimonarchial' originates from Modern English, specifically formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against') plus 'monarchial' (from Latin 'monarchia' via Old French 'monarchie'), where 'monarch-' comes from Greek 'monarkhes' meaning 'sole ruler'.

'antimonarchial' developed by combining 'anti-' with 'monarchial' (a variant of 'monarchical'). 'Monarchia' in Late Latin came from Greek 'monarkhia'; Middle English borrowed forms like 'monarchie' before the adjective forms 'monarchial/monarchical' and then negative formations such as 'anti-monarchial' or 'antimonarchical' appeared in modern English.

Initially it simply meant 'against monarchy' and over time has retained that core meaning, used to describe persons, movements, or positions opposed to monarchical institutions.