Retainer, for instance (3)
I believe the answer is:
fee
'retainer for instance' is the definition.
(I know that consideration is a type of fee)
This is all the clue.
(Other definitions for fee that I've seen before include "price" , "Sum payable to professional person for services" , "Sum payable to, say, barrister" , "Amount paid for job" , "Charge for professional services" .)