'nonbelligerent' is formed in English from the prefix 'non-' (from Latin 'non' meaning 'not') + 'belligerent' (from Latin). 'belligerent' itself derives from Latin elements related to 'bellum' (war) and 'gerere' (to wage).

'belligerent' comes from Latin 'belligerans'/'belligerant-' (present participle of 'belligerare', to wage war), via Late Latin and possibly Old French into Middle/Modern English as 'belligerent'. The compound 'non-' + 'belligerent' developed in Modern English to denote 'not belligerent'.

Originally centered on the idea of 'waging war' (from Latin roots), 'belligerent' came to mean 'hostile' or 'engaged in conflict'; 'nonbelligerent' has been used to indicate the absence of participation in hostilities or a refusal to take up arms, a meaning that has remained stable.