Solvent of very good quality (7)
I believe the answer is:
acetone
'solvent' is the definition.
(acetone is a kind of solvent)
'very good quality' is the wordplay.
'very good' becomes 'ace' (I've seen this before).
'quality' becomes 'tone' (synonyms).
'ace'+'tone'='ACETONE'
'of' is the link.
(Other definitions for acetone that I've seen before include "it dissolves" , "Paint thinner" , "Volatile stuff" , "chemical is the solution" , "Industrial solvent" .)