Dance club beside medium citadel causes irritation (10)
I believe the answer is:
discomfort
'irritation' is the definition.
(I know that irritation can be written as discomfort)
'dance club beside medium citadel' is the wordplay.
'dance club' becomes 'disco' (I've seen this before).
'beside' means one lot of letters go next to another (I've seen this in other clues).
'medium' becomes 'm' (as in UK clothing sizes).
'citadel' becomes 'fort' (a citadel is a fortified city).
'disco'+'m'+'fort'='DISCOMFORT'
'causes' is the link.
(Other definitions for discomfort that I've seen before include "pain" , "uneasiness" , "tenderness?" , "Unease" , "Slight anxiety" .)