Secures hair (5)
I believe the answer is:
locks
I believe this is a double definition.
'secures' is the first definition.
(locking is a kind of securing)
'hair' is the second definition.
(thesaurus)
(Other definitions for locks that I've seen before include "Tresses" , "Secure fasteners for doors" , "Securely fixes" , "Secures; person's hair" , "Door fasteners" .)