A criminal admits beginning to sell out (6)
I believe the answer is:
absent
'out' is the definition.
(thesaurus)
'a criminal admits beginning to sell' is the wordplay.
'criminal' becomes 'bent' (I've seen this before**).
'admits' is an insertion indicator.
'beginning to' suggests taking the first letters.
The initial letter of 'sell' is 's'.
'bent' placed around 's' is 'bsent'.
'a'+'bsent'='ABSENT'
(Other definitions for absent that I've seen before include "nowhere to be seen" , "Inattentive" , "Missing, lacking" , "Not attending" , "Forgetful, with mind on other things" .)