Employs us at the rest centre (4)
I believe the answer is:
uses
'employs' is the definition.
('use' can be a synonym of 'employ')
'us at the rest centre' is the wordplay.
'at' is a charade indicator (letters next to each other).
'centre' means to look at the middle letters.
The centre of 'rest' is 'es'.
'us'+'es'='USES'
(Other definitions for uses that I've seen before include "Takes (drugs)" , "What an employer does" , "Customs" , "Functions, applications" , "Employs" .)