A column about Irish carrier (7)
I believe the answer is:
airline
'carrier' is the definition.
(airline is a kind of carrier)
'a column about irish' is the wordplay.
'column' becomes 'line' (I've seen this before).
'about' means one lot of letters go next to another.
'irish' becomes 'ir' (abbreviation).
'line' after 'ir' is 'irline'.
'a'+'irline'='AIRLINE'
(Other definitions for airline that I've seen before include "BA, say" , "Company providing scheduled flights" , "Transport organisation" , "It serves both divers and travellers" , "carrier" .)