Disciplined old criminal to stop breaking in (8)
I believe the answer is:
obedient
'disciplined' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?
'old criminal to stop breaking in' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'criminal' becomes 'bent' (I've seen this before).
'to stop' becomes 'die' (I've seen this in other clues).
'breaking in' is an insertion indicator.
'bent' placed around 'die' is 'bedient'.
'o'+'bedient'='OBEDIENT'
Can you help me to learn more?
(Other definitions for obedient that I've seen before include "Ready to agree" , "Deferential" , "Passive" , "Ready to comply" , "Complying with orders" .)