The Collaborative International Dictionary of English v.0.48:

Administrator \Ad*min`is*tra"tor\, n. [L.]
   1. One who administers affairs; one who directs, manages,
      executes, or dispenses, whether in civil, judicial,
      political, or ecclesiastical affairs; a manager.
      [1913 Webster]

   2. (Law) A man who manages or settles the estate of an
      intestate, or of a testator when there is no competent
      executor; one to whom the right of administration has been
      committed by competent authority.
      [1913 Webster]

WordNet (r) 3.0 (2006):

administrator
    n 1: someone who administers a business [syn: administrator,
         decision maker]
    2: the party appointed by a probate court to distribute the
       estate of someone who dies without a will or without naming
       an executor
    3: someone who manages a government agency or department [syn:
       administrator, executive]