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]