The Collaborative International Dictionary of English v.0.48:

Dispersive \Dis*pers"ive\, a.
   Tending to disperse.
   [1913 Webster]

   Dispersive power (Opt.), the relative effect of a material
      in separating the different rays of light by refraction,
      as when the substance is formed into a prism. --
      Dis*pers"ive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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