City has a key assistant (8)
I believe the answer is:
adelaide
'city' is the definition.
(Adelaide is an example)
'a key assistant' is the wordplay.
'key' becomes 'del' (del key on a keyboard).
'assistant' becomes 'aide' (aide is a kind of assistant).
'a'+'del'+'aide'='ADELAIDE'
'has' acts as a link.
(Other definitions for adelaide that I've seen before include "State capital of South Australia" , "Lead aide to Oz" , "where there was recently a test" , "old consort" , "Lead aide out to Australia" .)