Flammable liquid ruined hat after hot vessel tipped over (7)
I believe the answer is:
naphtha
'flammable liquid' is the definition.
'ruined hat after hot vessel tipped over' is the wordplay.
'ruined' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'hot' becomes 'h'.
'vessel' becomes 'pan' (I have seen 'Shallow vessel ' mean 'pan' so perhaps 'vessel' could also mean 'pan').
'tipped over' shows that the letters should be reversed in order.
'h'+'pan'='hpan'
'hpan' backwards is 'naph'.
'hat' anagrammed gives 'tha'.
'tha' after 'naph' is 'NAPHTHA'.
(Other definitions for naphtha that I've seen before include "Rock-oil" , "Flammable oil from wood, coal tar, etc" , "Flammable liquid hydrocarbon mixture" , "Inflammable oil" , "fiery mixture" .)