Solvent, wicked quality (7)
I believe the answer is:
acetone
'solvent' is the definition.
(acetone is a kind of solvent)
'wicked quality' is the wordplay.
'wicked' becomes 'ace' (ace can informally mean very good).
'quality' becomes 'tone' (synonyms).
'ace'+'tone'='ACETONE'
(Other definitions for acetone that I've seen before include "Inflammable liquid" , "Colourless solvent" , "Paint thinner" , "chemical is the solution" , "Industrial solvent" .)