\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.

\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.

\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.

\Tre*pan"\, v. t.
To insnare; to trap; to trapan.
      Guards even of a dozen men were silently trepanned from
      their stations.                          --De Quincey.