Benny's cool, not cold (4)
I believe the answer is:
hill
'benny's' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'cool not cold' is the wordplay.
'cool' becomes 'chill' (synonyms).
'not' suggests deleting specific letters.
'cold' becomes 'C' (eg on taps).
'chill' with 'c' removed is 'HILL'.
Can you help me to learn more?
(Other definitions for hill that I've seen before include "See 14" , "Gradient" , "Box ---, Emma picnic site (J.Austen)" , "Incline" , "Raised area of land" .)