The inference is, it's a discount (9)
I believe the answer is:
deduction
I believe this is a double definition.
'the inference' is the first definition.
(deduction is a kind of inference)
'it's a discount' is the second definition.
('deduction' can be a synonym of 'discount')
'is' is the link.
(Other definitions for deduction that I've seen before include "Conclusion" , "Removal; finding" , "Taking off" , "Amount taken away" , "Inference; stoppage" .)