Declines to overlook official applications (4)
I believe the answer is:
uses
'applications' is the definition.
(I've seen this before)
'declines to overlook official' is the wordplay.
'declines' becomes 'refuses' ('refuse' can be a synonym of 'decline').
'to overlook' indicates named letters should be taken away.
'official' becomes 'ref' (match official in football, say).
'refuses' with 'ref' removed is 'USES'.
(Other definitions for uses that I've seen before include "Employs" , "Purposes; consumes" , "deployments" , "Takes (drugs)" , "Consumes; treats" .)