The Collaborative International Dictionary of English v.0.48:

collectivize \col*lec"tiv*ize\ v. t.
   to bring under collective control; to organize for operation
   by the principles of collectivism; -- especially of farms and
   industrial enterprises.

   Syn: collectivise.
        [Webster 1913 Suppl. + WordNet 1.5]

WordNet (r) 3.0 (2006):

collectivize
    v 1: bring under collective control; of farms and industrial
         enterprises [syn: collectivize, collectivise]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "collectivize":
   annex, attach, commandeer, communalize, communize, confiscate,
   distrain, expropriate, garnish, impound, impress, levy,
   nationalize, press, replevin, replevy, sequester, sequestrate,
   socialize