Solvent, yet less fat (7)
I believe the answer is:
thinner
I believe this is a double definition.
'solvent' is the first definition.
(synonyms)
'less fat' is the second definition.
('thin' can be the opposite of 'fat' so perhaps 'thinner' is reasonable for 'less fat')
'yet' is the link.
(Other definitions for thinner that I've seen before include "Diluting agent" , "Volatile liquid" , "Less fat" , "what one adds to paint" , "More sparse" .)