Firm agreement (7)
I believe the answer is:
compact
I believe this clue is a double definition.
'firm' is the first definition.
(similar in meaning)
'agreement' is the second definition.
(compact can mean an agreement)
(Other definitions for compact that I've seen before include "Tightly-knit, agreement" , "An official agreement" , "Neatly packed" , "Condense" , "Dense; agreement" .)