English river or a part of Ireland (4)
I believe the answer is:
aire
'english river' is the definition.
(I've seen this before)
'a part of ireland' is the wordplay.
'part of ireland' becomes 'ire' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'ire'='AIRE'
'or' is the link.
Can you help me to learn more?
(Other definitions for aire that I've seen before include "River running through Leeds" , "Northern English river, tributary of the Ouse" , "flower of Yorkshire" , "English flower" , "River of the Yorkshire dales" .)