Hotness, warmth (4)
I believe the answer is:
heat
I believe this clue is a double definition.
'hotness' is the first definition.
(I know that hotness can be written as heat)
'warmth' is the second definition.
(I know that warmth can be written as heat)
(Other definitions for heat that I've seen before include "Energy that causes a rise in temperature" , "Apply warmth" , "Get agitated" , "It's measured in therms" , "early round" .)