Tea once stirred becomes solvent (7)
I believe the answer is:
acetone
'solvent' is the definition.
(acetone is a kind of solvent)
'tea once stirred' is the wordplay.
'stirred' indicates an anagram.
'tea'+'once'='teaonce'
'teaonce' anagrammed gives 'ACETONE'.
'becomes' is the link.
(Other definitions for acetone that I've seen before include "Remover of nail polish" , "Inflammable liquid" , "Volatile stuff" , "Common solvent" , "it dissolves" .)