Stimulant for a N Ireland settlement (9)
I believe the answer is:
adrenalin
'stimulant' is the definition.
(I've seen this before)
'a n ireland settlement' is the wordplay.
'settlement' indicates an anagram.
'n'+'ireland'='nireland'
'nireland' anagrammed gives 'drenalin'.
'a'+'drenalin'='ADRENALIN'
'for' acts as a link.
(Other definitions for adrenalin that I've seen before include "Hormone secreted in response to fear" , "Metabolism-affecting hormone" , "that pumps you up" , "A secretion" , "Booster" .)