'nonpoisonous' originates from Modern English as a compound combining the prefix 'non-' (ultimately from Latin 'non' meaning 'not') with the adjective 'poisonous' (from Old French 'poison', from Latin 'potionem'/'potio' where 'potio' meant 'a drink' or 'potion').

'poison' entered English from Old French 'poison' (from Latin 'potionem'/'potio'); the adjective 'poisonous' developed in Middle English by adding the suffix '-ous' to that noun, and in Modern English the negative prefix 'non-' has been attached to form 'nonpoisonous'.

Originally related to 'poison' in the sense of a (dangerous) potion or substance; 'nonpoisonous' has consistently meant 'not possessing poison' and retains that basic meaning in modern usage.