'osmolarity' originates from Modern scientific formation (New Latin/English), specifically from the adjective 'osmolar' plus the noun-forming suffix '-ity'. 'osmolar' in turn relates to 'osmole', where 'osmo-' comes from Greek 'ὠσμός' (osmós).

'osmolarity' developed from 'osmolar' (adjective) which derived from 'osmole' (coined in 20th-century chemistry as 'osmo-' + 'mole'). 'osmole' ultimately traces to Greek 'ὠσμός' meaning 'push' or 'impulse' and was adapted into modern scientific terminology to denote an osmotic amount of substance.

Initially the Greek root 'osmós' meant 'push' or 'impulse'; over time the derived scientific terms ('osmole', 'osmolar', 'osmolarity') came to denote quantities and concentrations related to osmosis, with 'osmolarity' now specifically meaning concentration of osmotically active particles per liter.