Nativity scene beast (3)
I believe the answer is:
ass
'nativity scene beast' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ass that I've seen before include "Horse-type animal" , "Jennet" , "Transport for a wise man - or a fool" , "Small hoofed animal" , "Pompous fool or beast of burden" .)