The devil at Newgate, historically? (3,4)
I believe the answer is:
old nick
'the devil' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for old nick that I've seen before include "Satan" , "Alcatraz?" , "Scratch" , "spirit of evil" , "Newgate's" .)