Subject to choice? Not quite (5)
I believe the answer is:
topic
'subject' is the definition.
('topic' can be a synonym of 'subject')
'to choice? not quite' is the wordplay.
'choice?' becomes 'pick' ('pick' can be a synonym of 'choice').
'not quite' means to remove the last letter.
'pick' with its final letter taken away is 'pic'.
'to'+'pic'='TOPIC'
(Other definitions for topic that I've seen before include "Theme of discourse" , "Subject (of speech, etc)" , "Subject (of, eg, speech)" , "Subject (of a talk, etc)" , "Something to discuss" .)