Stars exactly evenly in agreement? (6)
I believe the answer is:
treaty
'agreement?' is the definition.
(treaty is a kind of agreement)
'stars exactly evenly' is the wordplay.
'evenly' means one should take alternating letters (even-numbered letters only).
'stars'+'exactly'='starsexactly'
The alternate letters of 'starsexactly' are 'TREATY'.
'in' is the link.
(Other definitions for treaty that I've seen before include "A pact between countries" , "Ratified agreement between states" , "Pact or agreement between nations" , "International agreement" , "Political or private agreement" .)