The Collaborative International Dictionary of English v.0.48:

Inspector \In*spect"or\, n. [L.: cf. F. inspecteur.]
   1. One who inspects, views, or oversees; one to whom the
      supervision of any work is committed; one who makes an
      official view or examination, as a military or civil
      officer; a superintendent; a supervisor; an overseer.
      [1913 Webster]

   2. A police officer, typically holding a rank one below
      superintendent, and in some cases in charge of several
      precincts; as, inspector Clousseau is investigating the
      case.
      [PJC]

   Inspector general (Mil.), a staff officer of an army, whose
      duties are those of inspection, and embrace everything
      relative to organization, recruiting, discharge,
      administration, accountability for money and property,
      instruction, police, and discipline.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inspector general
    n 1: a military officer responsible for investigations