One on spree ultimately not flipping solvent! (7)
I believe the answer is:
acetone
'solvent' is the definition.
(acetone is a kind of solvent)
'one on spree ultimately not flipping' is the wordplay.
'one' becomes 'ace' (ace has a value of one in some card games).
'on' says to put letters next to each other.
'ultimately' says to take the final letters.
'flipping' says the letters should be written in reverse.
The final letter of 'spree' is 'e'.
'not' reversed gives 'ton'.
'e' after 'ton' is 'tone'.
'ace'+'tone'='ACETONE'
(Other definitions for acetone that I've seen before include "Paint thinner" , "Common solvent" , "Colourless solvent" , "Industrial solvent" , "it dissolves" .)