Expending (5)
'expending' is the definition.
('use' can be a synonym of 'expend')
This is the entire clue.
(Other definitions for using that I've seen before include "having recourse to" , "Putting into service" , "Putting to a particular purpose" , "Utilising" , "Exercising" .)
'expending' is the definition.
(using up is a kind of expending)
This is the entire clue.
(Another definition for using up that I've seen is " Exhausting (resources)".)