Docile old criminal welcomes end (8)
I believe the answer is:
Here is my best explanation:
'docile old criminal welcomes end' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?
'docile old criminal welcomes end' is the subsidiary indication.
'docile old' becomes 'o' (common abbreviation eg in OE for Old English. I am not sure about the 'docile' bit.**).
'criminal' becomes 'bent' (I've seen this before).
'welcomes' indicates putting letters inside (in sense of 'invites in').
'end' becomes 'die'.
'bent' going around 'die' is 'bedient'.
(Other definitions for obedient that I've seen before include "Complying with commands", "submissive", "Ready to submit to authority", "Complying with orders", "Like monk", "A good dog should be", "Docile", "Submissive, biddable", "Compliant" and "Doing what one is told, compliant".)