'antimonarchism' originates from Modern English, specifically formed from the prefix 'anti-' (from Greek 'anti' meaning 'against') and 'monarchism' (from 'monarch' + the suffix '-ism'), where 'monarch' stems from Greek 'monarkhos' meaning 'single ruler'.

'monarch' changed from Greek 'monarkhos' to Late Latin/Latinized 'monarcha' and Old French 'monarque', then entered Middle English as 'monarch'; the suffix '-ism' was added in Modern English to form 'monarchism', and 'anti-' was prefixed in Modern English to create 'antimonarchism'.

Initially it literally meant 'against rule by a single ruler' and over time has remained essentially the same in modern usage as 'opposition to monarchy', often used in political or ideological contexts.