Enter into US business contract with ancient city (5)
I believe the answer is:
incur
'enter into' is the definition.
(I've seen this before)
'us business contract with ancient city' is the wordplay.
'us' becomes 'in' (I can't justify this - if you can you should believe this answer much more).
'business' becomes 'co'.
'contract' means to remove the last letter (contract can mean to shorten).
'with' says to put letters next to each other.
'ancient city' becomes 'ur'.
'co' with its final letter taken away is 'c'.
'in'+'c'+'ur'='INCUR'
Can you help me to learn more?
(Other definitions for incur that I've seen before include "Become subject to (something unwelcome)" , "Become liable to (something) through one's actions" , "Become liable to (costs)" , "Bring on as a consequence" , "Become subject to (penalty)" .)