'antiwar' is a compound formed from the Greek prefix 'anti-' and the English word 'war'; 'anti-' originates from Greek 'antí' meaning 'against', and 'war' ultimately comes via Old North French 'werre' (from Frankish '*werra').

'war' changed from Frankish '*werra' to Old North French 'werre', then into Middle English as 'werre/war' and eventually became modern English 'war'. The modern compound 'antiwar' is a 19th–20th century English formation combining 'anti-' + 'war'.

Initially the element 'anti-' meant 'against' and 'war' referred to armed conflict; 'antiwar' has consistently meant 'against war', though over time it also came to denote organized movements and political positions opposing specific wars.