Source : Webster's Revised Unabridged Dictionary (1913)

Trepan \Tre*pan"\, v. t. & i. [imp. & p. p. {Trepanned}; p. pr.
   & vb. n. {Trepanning}.] [Cf. F. tr['e]paner. See {Trepan} a
   saw.] (Surg.)
   To perforate (the skull) with a trepan, so as to remove a
   portion of the bone, and thus relieve the brain from pressure
   or irritation; to perform an operation with the trepan.

Trepan \Tre*pan"\, n. [See {Trapan}.]
   1. A snare; a trapan.

            Snares and trepans that common life lays in its way.
                                                  --South.

   2. a deceiver; a cheat.

            He had been from the beginning a spy and a trepan.
                                                  --Macaulay.

Trepan \Tre*pan"\, n. [F. tr['e]pan (cf. Sp. tr['e]pano, It.
   trepano, trapano), LL. trepanum, fr. Gr. ? a borer, auger,
   trepan, fr. ? to bore, ? a hole. Cf. {Trephine}.]
   1. (Surg.) A crown-saw or cylindrical saw for perforating the
      skull, turned, when used, like a bit or gimlet. See
      {Trephine}.

   2. (Mining) A kind of broad chisel for sinking shafts.

Trepan \Tre*pan"\, v. t.
   To insnare; to trap; to trapan.

         Guards even of a dozen men were silently trepanned from
         their stations.                          --De Quincey.

Source : WordNet®

trepan
     n 1: a surgical instrument used to remove sections of bone from
          the skull [syn: {trephine}]
     2: a drill for cutting circular holes around a center
     v : cut a hole with a trepan, as in surgery
     [also: {trepanning}, {trepanned}]