Daughter abandons casual affair for marriage? (8)
I believe the answer is:
alliance
'for marriage?' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for alliance that I've seen before include "A joining of forces" , "Marriage - union" , "Bond" , "League - treaty" , "Confederation" .)