More willing to use exit in back (7)
I believe the answer is:
readier
'more willing' is the definition.
('ready' can be similar in meaning to 'willing')
'exit in back' is the wordplay.
'exit' becomes 'die' (synonyms).
'in' is an insertion indicator.
'back' becomes 'rear' (similar in meaning).
'die' put inside 'rear' is 'READIER'.
'to use' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for readier that I've seen before include "More willing" , "more immediately available" , "More prepared" .)