What persistent criminal has accumulated! (6)
I believe the answer is:
record
'accumulated' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for record that I've seen before include "Best or worst performance" , "Facts known about a person - may be criminal" , "Written report - best so far!" , "Write down; music disc" , "Chronicle or log" .)