... left over from farewell performance? (4)
I believe the answer is:
song
'performance?' is the definition.
(song is a kind of performance)
'left over from farewell' is the wordplay.
I cannot quite understand how this works, but
'over' could be 'on' (I've seen this in other clues) and 'on' is located in the answer.
This explanation may well be incorrect...
(Other definitions for song that I've seen before include "Lied" , "Ballad, aria" , "Musical number" , "Ditty" , "Unnecessary fuss" .)