Under-the-table payment (5)
I believe the answer is:
bribe
'under-the-table payment' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bribe that I've seen before include "Corrupt payment" , "Sop" , "Illegal incentive" , "Oil the palm (of)" , "Dishonestly persuade" .)