The Collaborative International Dictionary of English v.0.48:

Commandeer \Com`man*deer"\, v. t. [imp. & p. p. Commandeered;
   p. pr. & vb. n. Commandeering.] [D. kommandeeren to
   command, in South Africa to commandeer, fr. F. commander to
   command. See Command.]
   1. (Mil.) To compel to perform military service; to seize for
      military purposes; -- orig. used of the Boers.
      [Webster 1913 Suppl.]

   2. To take arbitrary or forcible possession of. [Colloq.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

commandeer
    v 1: take arbitrarily or by force; "The Cubans commandeered the
         plane and flew it to Miami" [syn: commandeer, hijack,
         highjack, pirate]