No bother mostly cutting through concrete (7)
I believe the answer is:
refusal
'no' is the definition.
(refusing is saying no)
'bother mostly cutting through concrete' is the wordplay.
'bother' becomes 'fuss' (synonyms).
'mostly' means to remove the last letter (most but not all of the word).
'cutting through' is an insertion indicator.
'concrete' becomes 'real' (associated in meaning).
'fuss' with its final letter removed is 'fus'.
'fus' inserted inside 'real' is 'REFUSAL'.
(Other definitions for refusal that I've seen before include "Repudiation" , "Negation" , "Failure to accept" , "(Horse) failure to jump" , "Horse's action in declining to jump a fence" .)