Untroubled seeing vehicle needing energy for nothing (8)
I believe the answer is:
carefree
'untroubled' is the definition.
('carefree' can be similar in meaning to 'untroubled')
'vehicle needing energy for nothing' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'needing' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mc2).
'for nothing' becomes 'free' (I've seen this before).
'car'+'e'+'free'='CAREFREE'
'seeing' is the link.
(Other definitions for carefree that I've seen before include "insouciant" , "Unworried, happy-go-lucky" , "not concerned?" , "relaxed" , "Untroubled" .)