Without a worry in the world (8)
I believe the answer is:
carefree
'without a worry in the world' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for carefree that I've seen before include "Unconstrained" , "Happy and blithe - no worries" , "Without worry or responsibility" , "Unworried, happy-go-lucky" , "Free of trouble and worry" .)