Swear in debate there's no hell (4)
I believe the answer is:
cuss
'swear' is the definition.
(I know that swear can be written as cuss)
'debate there's no hell' is the wordplay.
'debate' becomes 'discuss' (to discuss something is to debate it).
'there's no' indicates named letters should be taken away.
'hell' becomes 'dis' (term for the underworld in Greek myth).
'discuss' with 'dis' taken out is 'CUSS'.
'in' acts as a link.
(Other definitions for cuss that I've seen before include "Stubborn person" , "Blaspheme" , "Use bad language (informal)" , "Swear (slang)" , "Oath; (annoying sort of) person" .)