A foreigner like Poirot (7)
I believe the answer is:
belgian
'a foreigner' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for belgian that I've seen before include "Nationality of Rene Magritte" , "Hercule Poirot's nationality" , "Eg, Brussels native" , "One from Liege, say" , "Bengali from a European state?" .)