Annual celebration (3,4)
'annual celebration' is the definition.
(I know that New Year is a holiday)
This is all the clue.
(Other definitions for new year that I've seen before include "different diary now?" , "January 1st" , "Early days?" , "Resolve now" , "This is only five days old" .)
'annual celebration' is the definition.
This is the entire clue.
(Other definitions for birthday that I've seen before include "Invisible threads?" , "Personal anniversary of origin" , "Anniversary celebration" , "Hardy bit (anag)" , "Natal day" .)
(Another definition for christmas party that I've seen is " annual event - with 29ac".)