'antimonarchically' originates from Modern English, specifically from the prefix 'anti-' + the adjective 'monarchical' with the adverbial suffix '-ly', where 'anti-' meant 'against' and 'monarchical' related to 'monarchy'.

'antimonarchically' was formed from the adjective 'antimonarchical' (ant i- + monarchical) by adding the adverbial suffix '-ly'. The adjective 'monarchical' derives from 'monarchy', which comes from Latin through Old French and ultimately from Greek 'monarkhia' ('monos' = 'one' + 'arkhein' = 'to rule').

Initially the components meant 'against' (anti-) and 'rule by one' (monarchy); combined they have come to mean 'in a manner opposed to monarchy', a meaning that has remained stable in modern usage.