'antimonarchical' originates from two elements: the prefix 'anti-' (from Greek 'anti', meaning 'against') and 'monarchical' (from Late Latin/Old French via Latin 'monarchia'/'monarchicus', ultimately from Greek 'monárkhēs' meaning 'sole ruler').

'antimonarchical' was formed in modern English by adding the prefix 'anti-' to the existing adjective 'monarchical' (which developed from Greek 'monárkhēs' → Late Latin 'monarchia'/'monarchicus' → Old French 'monarchique' → Middle English 'monarchic/monarchical'), producing the modern English 'antimonarchical'.

Initially, roots concerned 'one ruler' or 'monarchical' (relating to monarchy); with the addition of 'anti-' the meaning became 'against monarchy' (opposition to monarchical rule).