'antimilitaristic' originates from modern English formation combining the prefix 'anti-' (from Greek 'anti' meaning 'against') and the adjective 'militaristic' (formed from 'militarism' + the suffix '-istic'), where 'anti-' meant 'against' and 'militaristic' relates to military or militarism.

'militaristic' developed from 'militarism', which came into English via French 'militarisme' and ultimately from Latin 'militaris' meaning 'of soldiers' (from 'miles', 'soldier'). The negative formation 'anti-' + 'militaristic' produced the modern English 'antimilitaristic'.

Initially elements like Latin 'militaris' meant 'of soldiers'; over time 'militarism' came to mean an ideological preference for military values and power, and 'antimilitaristic' has meant 'opposed to militarism' since its formation without a major shift in the negative sense.