[Greek ōsmos, a push.]
Osmosis is the diffusion of a solvent through a semipermeable membrane into a more concentrated solution, so tending to equalise concentrations on both sides of the membrane. Words relating to this sense include osmolality, the number of osmotically effective dissolved particles per unit quantity of a solution; osmometer, an instrument for demonstrating or measuring osmotic pressure; osmoregulation, the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations.
Rarely, words in osmo- derive instead from Greek osmē, odour, as in osmic, the adjective relating to odours or the sense of smell, or osmium, a chemical element, which was named from the pungent smell of its tetroxide. See also the next entry.