Being English, sad character’s enthralled by US city (6)
I believe the answer is:
entity
'being' is the definition.
(I've seen this in other clues)
'english sad character's enthralled by us city' is the wordplay.
'english' becomes 'E' (abbreviation).
'sad character' becomes 'tit' (I am not sure about this - if you are sure you should believe this answer much more).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'us city' becomes 'NY' (abbreviation for New York).
'tit' placed into 'ny' is 'ntity'.
'e'+'ntity'='ENTITY'
Can you help me to learn more?
(Other definitions for entity that I've seen before include "Individual being" , "Object" , "Presence" , "A thing with distinct and independent existence" , "It exists as a separate thing" .)