A hot sort of curse (4)
I believe the answer is:
oath
'curse' is the definition.
('oath' can be a synonym of 'curse')
'a hot sort' is the wordplay.
'sort' indicates anagramming the letters.
'a'+'hot'='ahot'
'ahot' is an anagram of 'OATH'.
'of' acts as a link.
(Other definitions for oath that I've seen before include "A word with a witness" , "Solemn vow" , "Sworn promise" , "It's taken in court" , "in court, we take it" .)