Renunciation of an appointment when meeting Yankee (8)
I believe the answer is:
apostasy
'renunciation' is the definition.
('apostasy' can be a synonym of 'renunciation')
'an appointment when meeting yankee' is the wordplay.
'an' becomes 'a'.
'appointment' becomes 'post' (I've seen this before).
'when' becomes 'as'.
'meeting' is a charade indicator (letters next to each other).
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'a'+'post'+'as'+'y'='APOSTASY'
'of' is the link.
(Other definitions for apostasy that I've seen before include "Abandonment of religious faith" , "Abandonment of religious beliefs" , "Ditching faith" , "Abandonment of one's beliefs" , "services are abandoned because of this?" .)