Salary to retain staff is a joke (6)
I believe the answer is:
parody
'a joke' is the definition.
(thesaurus)
'salary to retain staff' is the wordplay.
'salary' becomes 'pay' (synonyms).
'to retain' is an insertion indicator.
'staff' becomes 'rod' (both can mean a stick or cane).
'pay' placed around 'rod' is 'PARODY'.
'is' acts as a link.
(Other definitions for parody that I've seen before include "Make a mockery" , "Humorous misrepresentation" , "Comic imitation of, say, well-known literary style" , "a lampoon or comic imitation" , "Spoof, lampoon" .)