Stop up in Irish city (4)
I believe the answer is:
cork
This clue is a double definition.
'stop up' is the first definition.
(corking is a kind of stopping up)
'irish city' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for cork that I've seen before include "One stops" , "Buoyant bark" , "Stopper - Irish port" , "Buoyant substance from a tree" , "Irish city or county" .)