'anticonstitutionally' originates from English, specifically formed from the adjective 'anticonstitutional' plus the adverbial suffix '-ly'. The adjective itself combines the prefix 'anti-' (from Greek 'anti', meaning 'against') with 'constitutional' (from Latin 'constitutio' via Medieval/Late Latin 'constitutionalis').

'anticonstitutionally' developed when the adverbial suffix '-ly' (from Old English '-lice', meaning 'like' or 'manner of') was attached to 'anticonstitutional'. 'Constitution' came into English from Latin 'constitutio' through Old French and Middle English, and 'anti-' was borrowed from Greek via Latin.

Initially the components meant 'against' + 'a setting up' (constitution), so the combined sense was 'against the constitution'; this basic meaning has been preserved, yielding the current adverbial sense 'in a manner contrary to the constitution'.