The Collaborative International Dictionary of English v.0.48:

Inquisitor \In*quis"i*tor\, n. [L.: cf. F. inquisiteur. See
   Inquire.]
   1. An inquisitive person; one fond of asking questions. [R.]
      "Inquisitors are tatlers." --Feltham.
      [1913 Webster]

   2. (Law) One whose official duty it is to examine and
      inquire, as coroners, sheriffs, etc. --Mozley & W.
      [1913 Webster]

   3. (R.C.Ch.) A member of the Court of Inquisition.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inquisitor
    n 1: a questioner who is excessively harsh [syn: inquisitor,
         interrogator]
    2: an official of the ecclesiastical court of the Inquisition