Shorten a fixed agreement (8)
I believe the answer is:
contract
This clue could be a double definition.
'shorten' is the first definition.
(I know that shorten can be written as contract)
'a fixed agreement' is the second definition.
'contract' can be an answer for 'agreement' (contract is a kind of agreement). I'm not certain of the 'a fixed' bit.
Can you help me to learn more?
(Other definitions for contract that I've seen before include "type of bridge" , "Document setting out terms of agreement" , "four spades, perhaps" , "Agreement - lessen" , "Shrink in written agreement" .)