The Collaborative International Dictionary of English v.0.48:

deputize \dep"u*tize\ (d[e^]p"[-u]*t[imac]z), v. t.
   To appoint as one's deputy; to empower to act in one's stead;
   to appoint as one's substitute; to depute.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deputize
    v 1: act as a substitute; "She stood in for the soprano who
         suffered from a cold" [syn: substitute, deputize,
         deputise, step in]
    2: appoint as a substitute [syn: depute, deputize,
       deputise]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "deputize":
   accredit, act for, answer for, appear for, arm, assign, authorize,
   back up, charge, charter, clothe, clothe with power, commission,
   commit, consign, delegate, depute, designate an agent, detach,
   detail, devolute, devolve, devolve upon, empower, enable, endow,
   endue, entrust, front for, give in charge, invest, license,
   mission, pinch-hit for, post, represent, send out, speak for,
   stand in for, substitute for, transfer, understudy, warrant