Secure, as a ship (4)
I believe the answer is:
moor
'secure as a ship' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for moor that I've seen before include "Heathery upland" , "Heath - a North African Muslim" , "Berth, tie up" , "'On Ilka - - baht'at'" , "Open expanse covered with heather and bracken" .)