The Collaborative International Dictionary of English v.0.48:

doorstop \door"stop`\, n. (Carp.)
   The block or strip of wood or similar material which stops,
   at the right place, the shutting of a door; any object used
   to stop open doors from moving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

doorstop
    n 1: a stop that keeps open doors from moving [syn: doorstop,
         doorstopper]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "doorstop":
   arrest, bearing rein, bit, brake, chain, check, checkrein, chock,
   clog, countercheck, curb, curb bit, damper, drag, drag sail,
   drift anchor, drift sail, drogue, fetter, holdback, martingale,
   pelham, remora, scotch, sea anchor, shackle, snaffle, spoke, stay,
   stop, trammel



The Jargon File (version 4.4.7, 29 Dec 2003):

doorstop
 n.

    Used to describe equipment that is non-functional and halfway expected to
    remain so, especially obsolete equipment kept around for political reasons
    or ostensibly as a backup. Compare boat anchor.


The Free On-line Dictionary of Computing (30 December 2018):

doorstop

   Used to describe equipment that is non-functional and halfway
   expected to remain so, especially obsolete equipment kept
   around for political reasons or ostensibly as a backup.  "When
   we get another Wyse-50 in here, that ADM 3 will turn into a
   doorstop."

   Compare boat anchor.

   [Jargon File]