Champion melody impressing member (7)
I believe the answer is:
tribune
'champion' is the definition.
(I've seen this before)
'melody impressing member' is the wordplay.
'melody' becomes 'tune' (synonyms).
'impressing' means one lot of letters goes inside another (impress historically meant to conscript).
'member' becomes 'rib' (I have seen 'structural member' mean 'rib' so perhaps 'member' could also mean 'rib').
'tune' enclosing 'rib' is 'TRIBUNE'.
(Other definitions for tribune that I've seen before include "Official in ancient Rome" , "Classic guardian?" , "Ancient Roman official, church dais" , "Champion of the people" , "basilica" .)