the.com/osmolarity

means A measure of the concentration of dissolved particles in a solution, expressed as the number of solute particles per liter — the key number determining which way water will flow across a membrane.

from Built from 'osmo-,' referring to osmosis, which itself traces to Greek 'osmos' meaning 'push' or 'thrust' (itself from 'othein,' to push), plus the chemistry suffix '-arity' seen in words like 'molarity.' Osmosis was named in the 1800s for the pushing, driving action of fluid moving through a membrane toward the more concentrated side — osmolarity is simply the measured quantity behind that push.