Belief in a girl (5)
I believe the answer is:
faith
I believe this clue is a double definition.
'belief' is the first definition.
(faith is a kind of belief)
'a girl' is the second definition.
'in' is the link.
(Other definitions for faith that I've seen before include "A woman" , "Religious belief" , "Trust in someone" , "Unshakeable belief" , "'..... will move mountains'" .)