'antiparliamental' originates from Greek (the prefix 'anti-' from Greek 'ἀντί' meaning 'against') combined with English 'parliamental' (from 'parliament').

'parliament' entered English from Old French 'parlement' (from the verb 'parler', to speak); 'parlement' developed into Middle English 'parlement'/'parliament', and later the adjective 'parliamental' produced the compound with 'anti-' to form 'antiparliamental' in modern English.

Initially it meant 'against parliament' (literally opposed to a parliamentary body); over time it has retained that core meaning and is used to describe opposition to parliamentary institutions or principles.