Greek behind corruption (5)
I believe the answer is:
graft
'corruption' is the definition.
(thesaurus)
'greek behind' is the wordplay.
'greek' becomes 'gr'.
'behind' becomes 'aft' ('aft' can be a synonym of 'behind'**).
'gr'+'aft'='GRAFT'
(Other definitions for graft that I've seen before include "Slip" , "Hard work - corrupt profit" , "Hard work - illicit gain" , "Surgical transplant" , "Labour" .)