Margin notes possibly make things hot (9)
I believe the answer is:
brimstone
'things hot' is the definition.
I can't tell whether this definition defines the answer.
'margin notes possibly' is the wordplay.
'margin' becomes 'brim' (I've seen this in another clue).
'possibly' indicates an anagram.
'notes' anagrammed gives 'stone'.
'brim'+'stone'='BRIMSTONE'
'make' acts as a link.
Can you help me to learn more?
(Other definitions for brimstone that I've seen before include "Biblical sulphur that rained with fire on evil cities" , "Insect" , "hellish punishment" , "Old name for sulphur" , "Sulphur; butterfly" .)