'nonaggressionist' originates from modern English, specifically the elements 'non-' + 'aggression' + the suffix '-ist', where 'non-' meant 'not', 'aggression' comes from Late Latin 'aggressio' (attack), and '-ist' denotes 'one who advocates or practices'.

'aggression' entered English from Late Latin 'aggressio' (from the verb 'aggredi', 'to approach, attack'), via Old French/Middle English; the negative prefix 'non-' (from Latin 'non') was attached to form 'nonaggression' in modern English (cf. 'non-aggression pact'), and the agentive suffix '-ist' was later added to create 'nonaggressionist'.

Initially the root ('aggredi'/'aggressio') carried the sense of 'approach' or 'step toward' and later 'attack'; over time 'aggression' came to mean 'hostile action', and 'nonaggressionist' developed to mean 'one who opposes initiating force' or someone who supports policies of not initiating aggression.