City on the Irtysh River (4)
I believe the answer is:
omsk
'city on the irtysh river' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for omsk that I've seen before include "Russian city" , "City of Asian Russia" , "Russian port" , "Womble" , "City of south central Russia" .)