Check the mast rope (4)
I believe the answer is:
stay
I believe this clue is a triple definition!
'check' is the first definition.
(I know that stay is a more specific form of the action check)
'the mast' is the second definition.
(thesaurus)
'rope' is the third definition.
(thesaurus)
(Other definitions for stay that I've seen before include "Remain behind" , "Corset strut" , "Stanchion" , "Wait" , "Rope bracing a mast etc" .)