Vassal's superior, grand persona sent up in song (5,4)
I believe the answer is:
liege lord
'vassal's superior' is the definition.
'grand persona sent up in song' is the wordplay.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'persona' becomes 'role' ('role' can be a synonym of 'persona').
'sent up' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'song' becomes 'lied' (lied is a kind of song**).
'role' written backwards gives 'elor'.
'g'+'elor'='gelor'
'gelor' placed within 'lied' is 'LIEGE-LORD'.
(Another definition for liege lord that I've seen is " Oil ledger (anag) - feudal superior".)