Loyal Irishman's nervous reaction, imbibing port (9)
I believe the answer is:
patriotic
'loyal' is the definition.
('patriotic' can be a synonym of 'loyal')
'irishman's nervous reaction imbibing port' is the wordplay.
'irishman' becomes 'pat'.
'nervous reaction' becomes 'tic' (I've seen this in other clues).
'imbibing' indicates putting letters inside.
'port' becomes 'rio' (I've seen this before).
'pat'+'tic'='pattic'
'pattic' placed around 'rio' is 'PATRIOTIC'.
(Other definitions for patriotic that I've seen before include "Devoted to one's country" , "Having love for one's country" , "Loyal" , "Supporting the state" , "flag-waving?" .)