Employs punsters now and then (4)
I believe the answer is:
uses
'employs' is the definition.
('use' can be a synonym of 'employ')
'punsters now and then' is the wordplay.
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
The alternate letters of 'punsters' are 'USES'.
(Other definitions for uses that I've seen before include "Functions, applications" , "Puts into service" , "Operates" , "deployments" , "Employs" .)