Real Dictionary

osmosis in American English
the tendency of a solvent to pass through a semipermeable membrane, as the wall of a living cell, into a solution of higher concentration, so as to equalize concentrations on both sides of the membrane
noun: the tendency of a fluid, usually water, to pass through a semipermeable membrane into a solution where the solvent concentration is higher, thus equalizing the concentrations of materials on either side of the membrane

osmosis in British English
noun: the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration