Its possible link is with heat treatment (4)
I believe the answer is:
kiln
'heat treatment' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'its possible link is' is the wordplay.
'link' can be anagrammed to 'KILN'.
However, I am unsure how the anagram is indicated.
'with' is the link.
Can you help me to learn more?
(Other definitions for kiln that I've seen before include "Oven for firing bricks" , "Large commercial oven" , "Oven for firing ceramics etc" , "Large oven, for potters say" , "Furnace, oven" .)