Former love meets American aboard Delta flight (6)
I believe the answer is:
exodus
'flight' is the definition.
(exodus is a kind of flight)
'former love meets american aboard delta' is the wordplay.
'former' becomes 'ex'.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'meets american' becomes 'us' (I am not sure about this - if you are sure you should believe this answer much more).
'aboard' indicates putting letters inside (the inserted letters climb 'aboard').
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'o'+'us'='ous'
'ous' placed around 'd' is 'odus'.
'ex'+'odus'='EXODUS'
(Other definitions for exodus that I've seen before include "Film of book" , "Act of mass departure" , "Mass departure of people, as in 2nd Book of O. T." , "sequel to first one" , "OT book - flight" .)