A number can be hot stuff (5)
I believe the answer is:
cloth
'stuff' is the definition.
(thesaurus)
'a number can be hot' is the wordplay.
'a number can' becomes 'clot' (I can't explain this - if you can you should give a lot more credence to this answer).
'be hot' becomes 'h' (abbreviation eg on taps).
'clot'+'h'='CLOTH'
Can you help me to learn more?
(Other definitions for cloth that I've seen before include "Woven material" , "Gingham, say" , "The clergy" , "rag" , "Fabric, textile" .)