Ordered beer at discount (6)
I believe the answer is:
rebate
'discount' is the definition.
(rebating is a kind of discounting)
'ordered beer at' is the wordplay.
'ordered' indicates an anagram.
'beer'+'at'='beerat'
'beerat' anagrammed gives 'REBATE'.
(Other definitions for rebate that I've seen before include "Cash refund" , "Sum paid back" , "Return of, eg, tax" , "price reduction" , "(Eg, tax) refund" .)