Efficacious.
Untroubled.
Buoyant.
Radiant.
Jocular.
Carefree.
Bli­the.
Pleased.
Contented.
Gratified.

They all are they opposite of subside.
What do they mean?

Big words are like a different language,
But the bigness doesn't need explaining.

All you have to do to understand is,
Look them up.