Unloading vessel carrying less weight (7)
I believe the answer is:
lighter
This clue might be a double definition.
'unloading vessel' is the first definition.
'lighter' can be an answer for 'vessel' (lighter is a kind of vessel). I'm unsure of the 'unloading' bit.
'carrying less weight' is the second definition.
(lighter means less heavy)
Can you help me to learn more?
(Other definitions for lighter that I've seen before include "The girl (anag.)" , "relieved of some cargo?" , "Flat-bottomed barge - not so heavy" , "Vessel" , "Flat-bottomed boat" .)