The Collaborative International Dictionary of English v.0.48:

dungeon \dun"geon\ (d[u^]n"j[u^]n), n. [OE. donjoun highest
   tower of a castle, tower, prison, F. donjon tower or platform
   in the midst of a castle, turret, or closet on the top of a
   house, a keep of a castle, LL. domnio, the same word as LL.
   dominus lord. See Dame, Don, and cf. Dominion,
   Domain, Demesne, Danger, Donjon.]
   A close, dark prison, commonly, under ground, as if the lower
   apartments of the donjon or keep of a castle, these being
   used as prisons.
   [1913 Webster]

         Down with him even into the deep dungeon. -- Tyndale.
   [1913 Webster]

         Year after year he lay patiently in a dungeon. --
                                                  Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dungeon \Dun"geon\, v. t.
   To shut up in a dungeon. --Bp. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dungeon
    n 1: the main tower within the walls of a medieval castle or
         fortress [syn: keep, donjon, dungeon]
    2: a dark cell (usually underground) where prisoners can be
       confined

The Free On-line Dictionary of Computing (19 January 2023):

Zork
Dungeon

    /zork/ The second of the great early experiments in
   computer fantasy gaming; see ADVENT.  Zork was originally
   written on MIT-DM during the late 1970s, later distributed
   with BSD Unix as a patched, sourceless RT-11 Fortran
   binary (see retrocomputing) and commercialised as "The Zork
   Trilogy" by Infocom.  The Fortran source was later rewritten
   for portability and released to Usenet under the name
   "Dungeon".

   Both Fortran "Dungeon" and translated C versions are
   available from many FTP archives.

   [Jargon File]

   (1998-09-21)