Headwear worn by English cook (4)
I believe the answer is:
heat
'cook' is the definition.
(I've seen this before)
'headwear worn by english' is the wordplay.
'headwear' becomes 'hat' (I've seen this before).
'worn by' indicates putting letters inside (outside letters are worn by those on the inside).
'english' becomes 'e' (abbreviation).
'hat' placed around 'e' is 'HEAT'.
(Other definitions for heat that I've seen before include "Energy that caues a rise in temperature" , "Vehemence" , "Preliminary race to qualify finalists" , "Level of spice" , "eliminating round" .)