Coil on sink offers security measure (8)
I believe the answer is:
lockdown
'security measure' is the definition.
(I've seen this before)
'coil on sink' is the wordplay.
'coil' becomes 'lock'.
'on' says to put letters next to each other.
'sink' becomes 'down'.
'lock'+'down'='LOCKDOWN'
'offers' acts as a link.
(Other definitions for lockdown that I've seen before include "Act of confining prisoners to their cells" , "Security measure in prison" .)