Definition of dinosaur noun from the Oxford Advanced Learner's Dictionary

dinosaur

noun
ˈdaɪnəsɔː(r)
 
; ˈdaɪnəsɔːr
 
 
1 an animal that lived millions of years ago but is now extinct (= it no longer exists). There were many types of dinosaur, some of which were very large.2 (disapproving) a person or thing that is old-fashioned and cannot change in the changing conditions of modern life