Drunk vocalist forgetting verse is indifferent (7)
I believe the answer is:
stoical
'indifferent' is the definition.
(thesaurus)
'drunk vocalist forgetting verse' is the wordplay.
'drunk' is an anagram indicator.
'forgetting' suggests deleting specific letters.
'verse' becomes 'v'.
'vocalist' with 'v' taken away is 'ocalist'.
'ocalist' anagrammed gives 'STOICAL'.
'is' acts as a link.
(Other definitions for stoical that I've seen before include "showing passive acceptance" , "Indifferent to pain and pleasure" , "Long-suffering" , "resigned to suffering" , "Able to bear pain" .)