osmosis

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

• noun Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal solute concentration on both sides of the membrane.
• noun The tendency of fluids to diffuse in such a manner.
• noun A gradual, often unconscious process of assimilation or absorption.

from The Century Dictionary.

• noun The diffusion of fluids through membranes. See osmose.

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

• noun The tendency in fluids to mix, or become equably diffused, when in contact. It was first observed between fluids of differing densities, and as taking place through a membrane or an intervening porous structure. An older term for the phenomenon was Osmose.
• noun The action produced by this tendency.

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

• noun The net movement of solvent molecules from a region of high solvent potential to a region of lower solvent potential through a partially permeable membrane
• noun slang Picking up knowledge accidentally, without actually seeking that particular knowledge.

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

• noun (biology, chemistry) diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal