The Collaborative International Dictionary of English v.0.48:

Dinosaur \Di"no*saur\, Dinosaurian \Di`no*sau"ri*an\, n. [Gr. ?
   terrible + ? lizard.] (Paleon.)
   One of the Dinosauria. [Written also deinosaur, and
   deinosaurian.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

dinosaur
    n 1: any of numerous extinct terrestrial reptiles of the
         Mesozoic era

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

dinosaur

   1. Any hardware requiring raised flooring and special power.
   Used especially of old minicomputers and mainframes, in
   contrast with newer microprocessor-based machines.

   In a famous quote from the 1988 Unix EXPO, Bill Joy compared
   the liquid-cooled mainframe in the massive IBM display with
   a grazing dinosaur "with a truck outside pumping its bodily
   fluids through it".  IBM was not amused.

   Compare big iron; see also dinosaurs mating.

   2. [IBM] A very conservative user; a zipperhead.

   [Jargon File]


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

dinosaur
 n.

    1. Any hardware requiring raised flooring and special power. Used
    especially of old minis and mainframes, in contrast with newer
    microprocessor-based machines. In a famous quote from the 1998 Unix EXPO,
    Bill Joy compared the liquid-cooled mainframe in the massive IBM display
    with a grazing dinosaur “with a truck outside pumping its bodily fluids
    through it”. IBM was not amused. Compare big iron; see also mainframe.

    2. [IBM] A very conservative user; a zipperhead.