Write about melody from The Planets (7)
I believe the answer is:
neptune
'planets' is the definition.
(I know that Neptune is a Jovian planet)
'write about melody' is the wordplay.
'write' becomes 'pen' (synonyms).
'about' is a reversal indicator.
'melody' becomes 'tune' (synonyms).
'pen' backwards is 'nep'.
'nep'+'tune'='NEPTUNE'
'from the' is the link.
(Other definitions for neptune that I've seen before include "Eighth planet from the Sun" , "World" , "Sea god - outer planet" , "Roman god of the sea, with trident" , "extract from The Planets" .)