Applies (6)
'applies' is the definition.
('use' can be a synonym of 'apply')
This is the entire clue.
(Other definitions for uses that I've seen before include "Customs" , "Employments" , "What an employer does" , "Exercises" , "Consumes; treats" .)
'applies' is the definition.
(exerting is a kind of applying)
This is the entire clue.
(Other definitions for exerts that I've seen before include "Makes strenuous effort" , "Forcefully applies (pressure)" , "Brings into use or to bear" , "Brings into use, say strength" , "Brings something to bear forcefully" .)