'antirepublican' originates from English, formed from the prefix 'anti-' (from Greek 'antí' meaning 'against') and 'republican' (ultimately from Latin 'res publica', 'public thing').

'republican' passed into English from French 'républicain' (from Latin 'res publica'); the combining prefix 'anti-' (from Greek) was attached in English to form 'antirepublican' to mean 'against a republican'.

Initially, formations like 'antirepublican' primarily meant 'against a republic' or 'against republican government'; over time the term has also come to be used specifically to indicate opposition to the (capitalized) Republican Party in contexts such as US politics.