interpenetration

from WordNet (r) 3.0 (2006)

interpenetration
    n 1: the action of penetrating between or among
    2: mutual penetration; diffusion of each through the other [syn:
       {interpenetration}, {permeation}]

from The Collaborative International Dictionary of English v.0.48

Interpenetration \In`ter*pen`e*tra"tion\, n.
   The act or process of penetrating between or within other
   substances; mutual penetration; also, the result of a process
   of interpenetration. --Milman.
   [1913 Webster +PJC]