Fighting to promote one connected with union (7)
I believe the answer is:
marital
'union' is the definition.
Although both the answer and definition are adjectives, I cannot see how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for marital that I've seen before include "Conjugal" , "Relating to union of husband and wife" , "Ram tail (anag.)" , "Relating to marriage" , "related to union" .)