Avails oneself of (4)
I believe the answer is:
uses
'avails oneself of' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for uses that I've seen before include "Exercises" , "Puts to a particular purpose" , "Utilises" , "Consumes; treats" , "'Purposes, functions (4)'" .)