'antimilitarist' originates from Modern English, specifically the prefix 'anti-' and the word 'militarist', where 'anti-' meant 'against' and 'militarist' derived from 'military' with the agentive suffix '-ist' meaning 'one associated with or supporting'.

'antimilitarist' developed as a compound in the late 19th to early 20th century, influenced by French formations such as 'antimilitariste' and by the term 'militarism' (French 'militarisme'), which in turn traces to Latin 'militaris' ('of soldiers' or 'military').

Initially it referred specifically to people or movements opposing the rise or policy of militarism; over time it has retained that core meaning and is still used to describe persons, movements, or views opposed to military influence or buildup.