In Armagh a stoic is dismayed (6)
I believe the answer is:
aghast
'is dismayed' is the definition.
(synonyms)
'in armagh a stoic' is the wordplay.
'in' indicates a hidden word.
'AGHAST' is hidden within 'armagh a stoic'.
(Other definitions for aghast that I've seen before include "Thunderstruck" , "Horror-struck" , "Struck with horror" , "Shocked, dumbfounded" , "Deeply dismayed" .)