Law enforcement groups have not finished (6)
I believe the answer is:
posses
'law' is the definition.
(I know this)
'have not finished' is the wordplay.
'have' becomes 'possess' (synonyms).
'not finished' means to remove the last letter.
'possess' with its final letter taken away is 'POSSES'.
'enforcement groups' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for posses that I've seen before include "law enforcers" , "forces for law and order" , "Sheriffs' men deputed to chase outlaws" .)