Regular guest is host for debate (5)
I believe the answer is:
argue
'for debate' is the definition.
(synonyms)
'regular guest is host' is the wordplay.
'is host' indicates a hidden word (I've seen 'hosts' mean this).
'ARGUE' is hidden within 'regular guest'.
(Other definitions for argue that I've seen before include "Debate, row" , "Fall out" , "Reason" , "Debate, contest verbally" , "Altercate" .)