Irish drink, dead smooth (6)
I believe the answer is:
ironed
'smooth' is the definition.
(similar in meaning)
'irish drink dead' is the wordplay.
'irish' becomes 'IR' (abbreviation for Irish).
'drink' becomes 'one' (eg 'a cold one').
'dead' becomes 'd' (abbreviation in government records).
'ir'+'one'+'d'='IRONED'
(Other definitions for ironed that I've seen before include "Smoothed clothes using heavy object" , "Decreased?" , "flattened" , "Had an evening out" , "Got rid of creases" .)