Any of the animals belonging to the clade Dinosauria, especially those that existed during the Triassic, Jurassic and Cretaceous periods and are now extinct. [from c. 1840]
(proscribed) Any extinct reptile, not necessarily belonging to Dinosauria, that existed between about 230 million and 65 million years ago.
(figuratively, colloquial) A person or organisation that is very old, has very old-fashioned views, or is not willing to change and adapt.
(figuratively, colloquial) Anything no longer in common use or practice.