Former partner raised fare to go on American flight (6)
I believe the answer is:
Here is my best explanation:
'flight' is the definition.
(exodus is a kind of flight)
'former partner raised fare to go on american' is the subsidiary indication.
'former partner' becomes 'ex' (**).
'raised' says the letters should be written backwards.
'fare' becomes 'do' ('do' can be a synonym of 'fare').
'to go on' means one lot of letters go next to another.
'american' becomes 'us'.
'do' backwards is 'od'.
(Other definitions for exodus that I've seen before include "Biblical departure", "8, Book 2", "A mass departure, as in O.T. book", "sequel to first one", "Act of mass departure", "journey", "A mass departure of people, as in Bible", "Mass evacuation", "Mass leaving" and "Mass departure of people as of Jews from Egypt".)