More buoyant match (7)
I believe the answer is:
lighter
'more buoyant' is the definition.
('light' can be similar in meaning to 'buoyant')
'match' is the wordplay.
I cannot really understand how this works, but
'match' could be 'light' (I've seen this before) and 'light' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lighter that I've seen before include "Flat-bottomed barge - not so heavy" , "The girl (anag.)" , "Substitute for match" , "Fire-raiser" , "Smoker's implement" .)