A quip about police taking diamonds back purposely (9)
I believe the answer is:
specially
'purposely' is the definition.
Both the definition and answer are adverbs. Perhaps there's a link between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for specially that I've seen before include "Particularly" , "For a particular purpose" .)