'nonthermalized' originates from modern English, specifically formed by the negative prefix 'non-' plus the verb 'thermalize', where 'non-' meant 'not' and 'thermalize' meant 'to bring into thermal equilibrium (to make thermal).'

'thermalize' developed from the adjective 'thermal' (from Greek 'thermos' meaning 'heat', via Latin and Middle French/modern English) with the verb-forming suffix '-ize'; 'non-' (a Latin/Old English negative prefix) was later attached to create 'nonthermalized' in technical usage.

Initially, elements of the root ('thermos'/'thermal') meant 'heat' or 'relating to heat'; over time the derived verb 'thermalize' came to mean 'to reach or be brought to thermal equilibrium', and 'nonthermalized' now specifically means 'not brought to thermal equilibrium' in scientific contexts.