The Collaborative International Dictionary of English v.0.48:

Diffusive \Dif*fu"sive\, a. [Cf. F. diffusif.]
   Having the quality of diffusing; capable of spreading every
   way by flowing; spreading widely; widely reaching; copious;
   diffuse. "A plentiful and diffusive perfume." --Hare.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diffusive
    adj 1: spreading by diffusion [syn: diffusing(a), diffusive,
           dispersive, disseminative]