Discount to be returned in the price (6)
I believe the answer is:
rebate
'discount' is the definition.
(I know that discount can be written as rebate)
'be returned in the price' is the wordplay.
'returned' says the letters should be written backwards.
'in the' is an insertion indicator.
'price' becomes 'rate' (I've seen this in other clues).
'be' backwards is 'eb'.
'eb' put into 'rate' is 'REBATE'.
'to' is the link.
(Other definitions for rebate that I've seen before include "Partial refund, reduction in payment" , "(Eg, tax) refund" , "Cash refund" , "Return of, eg, tax" , "Refund - discount" .)