No stir's endless imprisoned by concrete (7)
I believe the answer is:
refusal
'no' is the definition.
(thesaurus)
'stir's endless imprisoned by concrete' is the wordplay.
'stir's' becomes 'fuss' ('fuss' can be a synonym of 'stir').
'endless' means to remove the last letter.
'imprisoned by' is an insertion indicator.
'concrete' becomes 'real' ('real' can be similar in meaning to 'concrete').
'fuss' with its final letter taken away is 'fus'.
'fus' going inside 'real' is 'REFUSAL'.
(Other definitions for refusal that I've seen before include "regrets?" , "Negative response" , "Dissent" , "(Horse) failure to jump" , "The act of saying no" .)