The Collaborative International Dictionary of English v.0.48:

Intern \In*tern"\, a. [L. internus: cf. F. interne. See
   Internal.]
   Internal. [Obs.] --Howell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intern \In*tern"\, v. t. [F. interne. See Intern, a.]
   1. To put for safe keeping in the interior of a place or
      country; to confine to one locality; as, to intern troops
      which have fled for refuge to a neutral country.
      [1913 Webster]

   2. To hold until the end of a war, as enemy citizens in a
      country at the time of outbreak of hostilities; -- an
      action performed by countries.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

intern \in*tern"\, n. [F.] (F. pron. [a^]N`t[^a]rn")
   1. (Med.) A resident physician in a hospital, especially one
      who has recently received the Doctorate and is practising
      under supervision of experienced physicians, as a
      continuation of the training process; a house physician;
      also called houseman in Britain. [Also spelled
      interne.]
      [Webster 1913 Suppl. +PJC]

   2. A person working as an apprentice to gain experience in an
      occupation; sometimes the position is paid a salary, and
      other times it is not; as, a white house intern; an intern
      in a law firm.
      [PJC]

WordNet (r) 3.0 (2006):

intern
    n 1: an advanced student or graduate in medicine gaining
         supervised practical experience (`houseman' is a British
         term) [syn: intern, interne, houseman, medical
         intern]
    v 1: deprive of freedom; "During WW II, Japanese were interned
         in camps in the West"
    2: work as an intern; "The young doctor is interning at the
       Medical Center this year"

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "intern":
   Doctor of Medicine, GP, MD, addressee, allopath, allopathist,
   apprentice teacher, artist-in-residence, attending physician,
   bastille, bolt in, bosom, cast in prison, center, clap in jail,
   clap up, confine, constrain, core, coroner, country doctor,
   croaker, deepest recesses, denizen, doc, doctor, dweller,
   family doctor, gaol, general practitioner, graduate assistant,
   habitant, heart, heart of hearts, hold captive, hold in captivity,
   hold prisoner, house detective, house physician, immure, imprison,
   incarcerate, incumbent, inhabitant, inhabiter, inmate, inner,
   inner landscape, inner life, inner man, inner nature, inner recess,
   inner self, inpatient, inside, interior, interior man, internal,
   intrados, inward, jail, jug, leech, live-in maid, lock in, lock up,
   locum tenens, medical attendant, medical examiner, medical man,
   medical practitioner, medico, monitor, occupant, occupier,
   paraprofessional, penetralia, physician, physician in ordinary,
   practice teacher, praepostor, prefect, prison, proctor,
   pupil teacher, quod, recesses, residencer, resident,
   resident physician, residentiary, resider, sawbones, secret place,
   secret places, sojourner, soul, student assistant,
   teaching assistant, teaching fellow, teaching intern, tenant,
   throw into jail, treat, vital center, vitals