Christmas boxes very original (5)
I believe the answer is:
novel
'original' is the definition.
(similar in meaning)
'christmas boxes very' is the wordplay.
'christmas' becomes 'noel' (synonyms).
'boxes' is an insertion indicator (the outside letters must 'box' inside letters in).
'very' becomes 'v' (abbreviation).
'noel' placed around 'v' is 'NOVEL'.
(Other definitions for novel that I've seen before include "Volume of prose fiction" , "piece of writing" , "Romance - new" , "New and strange" , "Fresh" .)