The Collaborative International Dictionary of English v.0.48:

Permeation \Per`me*a"tion\, n.
   The act of permeating, passing through, or spreading
   throughout, the pores or interstices of any substance.
   [1913 Webster]

         Here is not a mere involution only, but a spiritual
         permeation and inexistence.              --Bp. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

permeation
    n 1: the process of permeating or infusing something with a
         substance [syn: permeation, pervasion, suffusion]
    2: mutual penetration; diffusion of each through the other [syn:
       interpenetration, permeation]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "permeation":
   brewing, decoction, diffusion, drench, drenching, ducking, dunking,
   imbruement, imbuement, impregnation, infiltration, infusion,
   injection, instillation, instillment, interpenetration, leaching,
   lixiviation, maceration, marination, overrunning, overspreading,
   overswarming, penetration, percolation, pervasion, pulping,
   saturation, seething, soak, soakage, soaking, sopping, souse,
   sousing, steeping, suffusion, transfusion