From The Collaborative International Dictionary of English v.0.48:

osmosis \os*mo"sis\ ([o^]z*m[=o]"s[i^]s), n. [NL., fr. Gr.
   'wsmo`s, equiv. to 'w^sis impulse, fr. 'wqei^n to push.]
   (Chemical Physics)
   (a) 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.

   Note: The more rapid flow from the thinner to the thicker
         fluid was then called endosmosis (formerly
         endosmose), and the opposite, slower current,
         exosmosis (formerly exosmose). Both are, however,
         results of the same force. Osmosis may be regarded as a
         form of molecular attraction, allied to that of
         adhesion. See also osmotic pressure.
   (b) The action produced by this tendency.
       [1913 Webster]
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