Secure part in Metropolitan chorus (6)
I believe the answer is:
anchor
'secure' is the definition.
(anchoring is a kind of securing)
'part in metropolitan chorus' is the wordplay.
'part in' says the answer is hidden in the clue.
'ANCHOR' can be found hidden inside 'metropolitan chorus'.
(Other definitions for anchor that I've seen before include "Device to hold a ship in place" , "secured by a fluke" , "One is often cast" , "It may be used to secure" , "Be moored" .)