Knight under wild party bird (5)
I believe the answer is:
raven
'bird' is the definition.
(raven is a kind of bird)
'knight under wild party' is the wordplay.
'knight' becomes 'N' (chess abbreviation).
'under' says to put letters next to each other (below, in a down clue).
'wild party' becomes 'rave' (a dance party).
'n' after 'rave' is 'RAVEN'.
(Other definitions for raven that I've seen before include "Hungrily devour" , "Species of crow" , "pig" , "Passerine bird" , "Flyer" .)