Nub: link with heat that's off, not on (11)
I believe the answer is:
unthinkable
'on' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'nub link with heat that's off' is the wordplay.
'with' says to put letters next to each other.
'that's off' is an anagram indicator.
'nub'+'link'+'heat'='nublinkheat'
'nublinkheat' is an anagram of 'UNTHINKABLE'.
'not' acts as a link.
Can you help me to learn more?
(Other definitions for unthinkable that I've seen before include "Inconceivable" , "Too unlikely to consider" , "it's out of the question" , "Preposterous" .)