'isoosmotic' originates from Greek and New Latin, specifically from the Greek element 'iso-' from 'isos' meaning 'equal' and from 'osmotic' ultimately from Greek 'ōsmōtikos' (from 'ōsmos') where 'ōsmos' meant 'a pushing or impulse (a thrust)'.

'isoosmotic' developed as a compound of 'iso-' + 'osmotic' (often written 'iso-osmotic' or 'isosmotic' in earlier scientific usage) and entered modern English usage via New Latin/scientific formations to give the adjective 'isoosmotic'.

Initially it denoted the idea of 'equal push' in terms of osmotic action; over time it became a technical term meaning 'having equal osmotic pressure' between solutions.