Iron or tin, say, that glows in some fires (7)
I believe the answer is:
element
'tin say that glows in some fires' is the definition.
'element' can be an answer for 'tin say' (tin is a kind of element). I am unsure of the rest of the definition.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for element that I've seen before include "Basic substance or feature" , "Comfort zone" , "part of a toaster" , "Basic chemical unit" , "Singular ingredient" .)