Flavour goes with old musical piece (5)
I believe the answer is:
tango
'musical piece' is the definition.
(I've seen this before)
'flavour goes with old' is the wordplay.
'flavour' becomes 'tang' (synonyms).
'goes with' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tang'+'o'='TANGO'
(Other definitions for tango that I've seen before include "Latin American dance (requiring two?)" , "Dance; letter T" , "reputedly takes two" , "T in radio alphabet" , "Dramatic ballroom dance from Argentina" .)