A note, played forte, is something heavenly (5)
I believe the answer is:
cloud
'something heavenly' is the definition.
I can't tell whether this definition defines the answer.
'a note played forte' is the wordplay.
'a note' becomes 'c' (musical note).
'played forte' becomes 'loud' (similar in meaning. I am not sure about the 'played' bit.).
'c'+'loud'='CLOUD'
'is' is the link.
Can you help me to learn more?
(Other definitions for cloud that I've seen before include "E.g. stratus" , "It hides the sun" , "Mass of vapour visible in the air" , "Cumulus, for example" , "Nebula" .)