Dine in serene atmosphere (3)
I believe the answer is:
eat
'dine' is the definition.
(I've seen this before)
'in serene atmosphere' is the wordplay.
'in' indicates a hidden word.
'EAT' can be found hidden inside 'serene atmosphere'.
(Other definitions for eat that I've seen before include "Devour" , "Use a knife and fork" , "Worry" , "Make food disappear" , "tolerate in diet" .)