Most composed songs performed about romantic engagements (8)

I believe the answer is:
sedatest
'most composed songs performed' is the definition.
I can't judge whether this definition defines the answer.
'about romantic engagements' is the wordplay.
'about' indicates putting letters inside.
'romantic' becomes 'set' (I can't explain this - if you can you should believe this answer much more).
'engagements' becomes 'dates' ('date' can be a synonym of 'engagement').
'set' enclosing 'dates' is 'SEDATEST'.
Can you help me to learn more?
(Another definition for sedatest that I've seen is " Most cool".)
