The Collaborative International Dictionary of English v.0.48:

decolonize \decolonize\ v. t.
   to grant independence to (a former colony). [Also spelled
   decolonise.]
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

decolonize \decolonize\ v. i.
   to release one's colonies and free them to become
   independednt nations; -- of nations. [Also spelled
   decolonise.]
   [PJC]

WordNet (r) 3.0 (2006):

decolonise
    v 1: grant independence to (a former colony); "West Africa was
         decolonized in the early 1960's" [syn: decolonize,
         decolonise] [ant: colonise, colonize]