Introduction to crabby old captive (5)
I believe the answer is:
caged
'captive' is the definition.
(thesaurus)
'introduction to crabby old' is the wordplay.
'introduction to' suggests taking the first letters.
'old' becomes 'aged' (similar in meaning).
The initial letter of 'crabby' is 'c'.
'c'+'aged'='CAGED'
(Other definitions for caged that I've seen before include "Cooped up" , "Confined behind bars" , "Shut up" , "in prison" , "In a zoo?" .)