Awful meal not hot initially — don't swallow it! (8)
I believe the answer is:
methanol
'don't swallow it' is the definition.
(methanol is toxic)
'awful meal not hot initially' is the wordplay.
'awful' indicates anagramming the letters.
'initially' suggests taking the first letters.
The initial letter of 'hot' is 'h'.
'meal'+'not'+'h'='mealnoth'
'mealnoth' anagrammed gives 'METHANOL'.
(Other definitions for methanol that I've seen before include "Form of alcohol" , "Dangerous product" , "Wood spirit" , "Toxic alcohol" .)