The Collaborative International Dictionary of English v.0.48:

Internment \In*tern"ment\, n. [F. internement. See Intern.]
   1. Confinement within narrow limits, -- as of foreign troops,
      to the interior of a country.
      [1913 Webster]

   2. Confining within a country for the duration of a war; --
      usually of citizens of a hostile power.
      [PJC]

WordNet (r) 3.0 (2006):

internment
    n 1: confinement during wartime
    2: the act of confining someone in a prison (or as if in a
       prison) [syn: imprisonment, internment]
    3: placing private property in the custody of an officer of the
       law [syn: impoundment, impounding, internment,
       poundage]