The Collaborative International Dictionary of English v.0.48:

Pervasion \Per*va"sion\ (p[~e]r*v[=a]"zh[u^]n), n. [L. pervasio.
   See Pervade.]
   The act of pervading, passing, or spreading through the whole
   extent of a thing. --Boyle.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "pervasion":
   decoction, diffusion, imbuement, impregnation, infiltration,
   infusion, instillation, instillment, interpenetration, marination,
   overrunning, overspreading, overswarming, penetration, permeation,
   saturation, soaking, steeping, suffusion, transfusion