Mob in speech or debate (5)
I believe the answer is:
horde
'mob' is the definition.
(horde can mean a mob or crowd of people)
'in speech or debate' is the wordplay.
'in' says the answer is hidden in the clue.
'HORDE' is hidden within 'speech or debate'.
(Other definitions for horde that I've seen before include "Host" , "Nomadic army" , "Large group of people" , "Great crowd" , "Many people" .)