Serious music disheartened grenadier on parade ground (5,5)
I believe the answer is:
grand opera
'serious music' is the definition.
(grand opera is a kind of serious music)
'disheartened grenadier on parade ground' is the wordplay.
'disheartened' means to remove the middle letters.
'ground' indicates anagramming the letters (grind the letters ).
'grenadier' with its middle removed is 'gr'.
'on'+'parade'='onparade'
'onparade' anagrammed gives 'andopera'.
'gr'+'andopera'='GRAND OPERA'
(Other definitions for grand opera that I've seen before include "major theatrical project" , "Piano concerti could be regarded as such" , "eg Aida, Faust" , "Lavish stage work" , "serious music" .)