Irritable declaration of one in Casualty? (9)
I believe the answer is:
impatient
'irritable' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
(Other definitions for impatient that I've seen before include "Fidgety" , "Irritable" , "Unlike Job" , "restive" , "not able to wait" .)