Component that provides heat (7)
I believe the answer is:
element
'component' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for element that I've seen before include "Basic chemical unit" , "(One's) preferred or natural environment" , "Singular ingredient" , "Basic constituent; aspect" , "iron or copper, perhaps" .)