Preserve farewell piece of music (7)
I believe the answer is:
cantata
'piece of music' is the definition.
(I've seen this before)
'preserve farewell' is the wordplay.
'preserve' becomes 'can' (canning is a kind of preserving).
'farewell' becomes 'ta ta' (I've seen this in another clue).
'can'+'tata'='CANTATA'
(Other definitions for cantata that I've seen before include "piece of music" , "One of 200+ by Bach" , "Sacred choral piece" , "Musical composition with religious text" , "Choral item" .)