Chat-room monitor rated room 'terrible' (9)
I believe the answer is:
moderator
'chat-room monitor' is the definition.
'rated room terrible' is the wordplay.
'terrible' indicates anagramming the letters.
'rated'+'room'='ratedroom'
'ratedroom' anagrammed gives 'MODERATOR'.
(Other definitions for moderator that I've seen before include "Overseer of exam" , "One presides over a forum or debate" , "Site foreman" , "Presbyterian minister - superintendent of university examinations" , "member of exam team" .)