'pacifist-leaning' originates from modern English, combining 'pacifist' (from French 'pacifiste', ultimately from Latin 'pax, pacis' meaning 'peace' plus the agent suffix '-ist') and 'leaning' (the present participle/adjectival form of 'lean', from Old English/Germanic roots meaning 'to incline').

'pacifist' entered English in the late 19th to early 20th century from French 'pacifiste'; 'lean' is an older Germanic word (Old English roots) that produced the adjectival form 'leaning'. The compound 'pacifist-leaning' is a modern English formation that arose by joining the noun/adjective 'pacifist' with the participial adjective 'leaning' to indicate tendency.

Initially, 'pacifist' referred to someone opposed to war or violence; 'leaning' meant 'inclination'. Over time the compound came to mean 'having an inclination toward pacifism' and is used to describe attitudes, policies, or people with that tendency.