Source : Webster's Revised Unabridged Dictionary (1913)

Diffusion \Dif*fu"sion\, n. [L. diffusio: cf. F. diffusion.]
   1. The act of diffusing, or the state of being diffused; a
      spreading; extension; dissemination; circulation;
      dispersion.

            A diffusion of knowledge which has undermined
            superstition.                         --Burke.

   2. (Physiol.) The act of passing by osmosis through animal
      membranes, as in the distribution of poisons, gases, etc.,
      through the body. Unlike absorption, diffusion may go on
      after death, that is, after the blood ceases to circulate.

   Syn: Extension; spread; propagation; circulation; expansion;
        dispersion.

Source : WordNet®

diffusion
     n 1: (physics) the process of diffusing; the intermingling of
          molecules in gases and liquids as a result of random
          thermal agitation
     2: the spread of social institutions (and myths and skills)
        from one society to another
     3: the property of being diffused or dispersed [syn: {dissemination}]
     4: the act of dispersing or diffusing something; "the
        dispersion of the troops"; "the diffusion of knowledge"
        [syn: {dispersion}, {dispersal}, {dissemination}]