Serene joy (5)
I believe the answer is:
bliss
'serene joy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bliss that I've seen before include "Serene joy" , "State of euphoria" , "Felicity" , "'Where ignorance is ....., 'tis folly to be wise'" , "Sir Arthur --, British composer" .)