Nobody in Rome raised warning (4)
I believe the answer is:
nemo
'nobody in rome' is the definition.
The definition suggests a singular noun which matches the answer.
'raised warning' is the wordplay.
'raised' shows that the letters should be reversed in order (going up in a down clue).
'warning' becomes 'omen' (I've seen this in another clue).
'omen' reversed gives 'NEMO'.
Can you help me to learn more?
(Other definitions for nemo that I've seen before include "- me impune lacessit (motto of Scotland)" , "Literary captain" , "Fish sought in film" , "Captain of the Nautilus" , "commander for the Nautilus" .)