Less heavy (7)
I believe the answer is:
lighter
'less heavy' is the definition.
('light' can be the opposite of 'heavy' so perhaps 'lighter' is reasonable for 'less heavy')
This is all the clue.
(Other definitions for lighter that I've seen before include "Kind of barge - carrying less?" , "Barge; flame producer" , "The girl (anag.)" , "carrying less cargo?" , "Cargo barge; smoker's accessory" .)