Nine drunk bores allowed to be forgiving (7)
I believe the answer is:
lenient
'be forgiving' is the definition.
(thesaurus)
'nine drunk bores allowed' is the wordplay.
'drunk' is an anagram indicator.
'bores' indicates putting letters inside (to bore something can mean to drill into it).
'allowed' becomes 'let' (to let is to allow or permit).
'nine' is an anagram of 'nien'.
'nien' inserted inside 'let' is 'LENIENT'.
'to' acts as a link.
(Other definitions for lenient that I've seen before include "Easy, soft" , "Showing tolerance" , "Indulgent, lax" , "'Indulgent, easy (7)'" , "Soft-hearted" .)