osmotic pressure

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The pressure exerted by the flow of water through a semipermeable membrane separating two solutions with different concentrations of solute.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physical Chemistry) The pressure which a solution of a substance in a liquid exerts on a semipermeable membrane, through which the solvent can diffuse but the dissolved substance (the solute) cannot diffuse, when separated across the membrane from the pure solvent. In general, the osmotic pressure will depend almost proportionally up to certain concentrations upon the molal concentration of the solute.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The hydrostatic pressure exerted by a solution across a semipermeable membrane from a pure solvent; the pressure needed to counteract osmosis

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (physical chemistry) the pressure exerted by a solution necessary to prevent osmosis into that solution when it is separated from the pure solvent by a semipermeable membrane