Sleeve sun’s heat, hard covering (6)
I believe the answer is:
sheath
'sleeve' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'sun's heat hard covering' is the wordplay.
'covering' says the answer is hidden in the clue.
'SHEATH' is hidden in the letters of 'suns heat hard'.
Can you help me to learn more?
(Other definitions for sheath that I've seen before include "coat" , "Protective cover" , "Cover protecting" , "(Blade's) cover" , "cocktail dress" .)