'nonhuman' originates from a combination of elements: the prefix 'non-' (from Latin 'non') where 'non' meant 'not', combined with 'human' (from Latin 'humanus').

'human' derives from Latin 'humanus', passed into Old French and Middle English as forms like 'humain'/'human' and eventually became the modern English 'human'. The compound 'nonhuman' arose in Modern English by combining the negative prefix 'non-' with 'human' to form 'nonhuman'.

Initially it literally meant 'not human'; over time the usage broadened to refer to a wide range of non-human entities (animals, machines, AIs, extraterrestrials, etc.) and contexts (ethical, legal, scientific).