Swine: chap always seen in celebration (8)
I believe the answer is:
hogmanay
'celebration' is the definition.
(I've seen this before)
'swine chap always' is the wordplay.
'swine' becomes 'hog' (hog is a kind of swine).
'chap' becomes 'man' (chap can mean a man).
'always' becomes 'ay' (archaic term for 'always').
'hog'+'man'+'ay'='HOGMANAY'
'seen in' acts as a link.
(Other definitions for hogmanay that I've seen before include "New Year's Eve in Scotland" , "Annual celebration" , "Scottish celebration framed in mahogany" , "Festival" , "New Year up north" .)