Poor city gets three keys (5)
I believe the answer is:
needy
'poor' is the definition.
('needy' can be similar in meaning to 'poor')
'city gets three keys' is the wordplay.
'city' becomes 'ny' (I've seen this in other clues).
'gets' is an insertion indicator (gets can mean captures or absorbs).
'three keys' becomes 'eed' (I can't justify this - if you can you should believe this answer much more).
'ny' going around 'eed' is 'NEEDY'.
Can you help me to learn more?
(Other definitions for needy that I've seen before include "Insecure; very poor" , "Poor - destitute" , "clinging" , "Necessitous" , "Impecunious" .)