Film star adding line to marriage vow (4)
I believe the answer is:
idol
'film star' is the definition.
(idol can mean a celebrity)
'line to marriage vow' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'marriage vow' becomes 'i do' (I've seen this in another clue).
'l' put after 'ido' is 'IDOL'.
'adding' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for idol that I've seen before include "As before, fake" , "Hero of screen or stage" , "Favourite" , "Object of reverence" , "pop star" .)