'nonisosmotic' originates from Modern English, specifically formed from the prefix 'non-' (from Latin 'non'), and 'isosmotic' (from New Latin/Greek 'isos' + 'osmos'), where 'non-' meant 'not', 'isos' meant 'equal', and 'osmos' meant 'push/impulse (relating to osmosis)'.

'isosmotic' derives from New Latin/Greek roots: Greek 'isos' (equal) + Greek 'osmōtikos' (relating to osmosis). In modern scientific English the prefix 'non-' was attached to 'isosmotic' to coin 'nonisosmotic' to indicate the opposite condition.

Initially, 'isosmotic' meant 'having equal osmotic pressure'; the modern formation 'nonisosmotic' has the clear, literal opposite meaning: 'not having equal osmotic pressure'.