Serious English style of music (5)
I believe the answer is:
grime
'style of music' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'serious english' is the wordplay.
'serious' becomes 'grim'.
'english' becomes 'E' (abbreviation as in OED).
'grim'+'e'='GRIME'
Can you help me to learn more?
(Other definitions for grime that I've seen before include "Dirt, grease" , "Muck" , "Filth, dirt" , "an ingrained phenomenon" , "Engrained dirt" .)