The subject to choose, almost (5)
I believe the answer is:
topic
'the subject' is the definition.
(as in a topic for discussion)
'to choose almost' is the wordplay.
'choose' becomes 'pick' (picking is a kind of choosing).
'almost' means to remove the last letter (most of the word but not all of it).
'pick' with its final letter removed is 'pic'.
'to'+'pic'='TOPIC'
(Other definitions for topic that I've seen before include "Theme of discourse" , "Subject (of, eg, speech)" , "Something to discuss" , "Subject matter of a conversation or discussion" , "Subject (of speech, etc)" .)