1. [n]  a power of attorney document given by shareholders of a corporation authorizing a specific vote on their behalf at a corporate meeting
2. [n]  a person authorized to act for another

PROXY is a 5 letter word that starts with P.

1. \Prox"y\, n.; pl. {Proxies}. [Contr. from procuracy. Cf.
   {Proctor}.]
   1. The agency for another who acts through the agent;
      authority to act for another, esp. to vote in a
      legislative or corporate capacity.
   
            I have no man's proxy: I speak only for myself.
                                                  --Burke.
   
   2. The person who is substituted or deputed to act or vote
      for another.
   
            Every peer . . . may make another lord of parliament
            his proxy, to vote for him in his absence.
                                                  --Blackstone.
   
   3. A writing by which one person authorizes another to vote
      in his stead, as in a corporation meeting.
   
   4. (Eng. Law) The written appointment of a proctor in suits
      in the ecclesiastical courts. --Burrill.
   
   5. (Eccl.) See {Procuration}. [Obs.]
   
   

2. \Prox"y\, v. i.
   To act or vote by proxy; to do anything by the agency of
   another. [R.]