Sailor with tourist trapping that man, one once terrifying in London (4,3,6)
I believe the answer is:
jack the ripper
'one once terrifying in london' is the definition.
The definition suggests a singular noun which matches the answer.
'sailor with tourist trapping that man' is the wordplay.
'sailor' becomes 'jack' (informal term for a sailor).
'with' says to put letters next to each other.
'tourist' becomes 'tripper' (tripper is a kind of tourist).
'trapping' indicates putting letters inside.
'that man' becomes 'he' (he refers to a man).
'tripper' enclosing 'he' is 'theripper'.
'jack'+'theripper'='JACK THE RIPPER'
Can you help me to learn more?
(Other definitions for jack the ripper that I've seen before include "Man with murderous intent" , "Victorian murderer" , "Victorian serial killer" , "Notorious murderer" , "Murderous character" .)