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]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "inquisitor":
   Paul Pry, Peeping Tom, asker, busybody, catechist,
   cross-interrogator, cross-questioner, detective, eavesdropper,
   examiner, gossip, inquirer, inquisitionist, inquisitive,
   interlocutor, interpellator, interrogator, interrogatrix,
   interviewer, nosy Parker, opinion-sampler, poller, pollster,
   prober, pry, querier, querist, questioner, questionist, quidnunc,
   quizzer, rubberneck, rubbernecker, sampler, scopophiliac,
   secret agent, sightseer, snoop, snooper, voyeur, yenta