Shake down (6)
I believe the answer is:
extort
'shake down' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for extort that I've seen before include "Using intimidation" , "Squeeze" , "Gain money by force" , "Take from by force or threat" , "Wring (money) out (by violence, etc)" .)