Bird's endlessly elegant (4)
I believe the answer is:
chic
'elegant' is the definition.
(thesaurus)
'bird's endlessly' is the wordplay.
'bird' becomes 'chick' (chick is a kind of bird).
'endlessly' means to remove the last letter.
'chick' with its last letter taken off is 'CHIC'.
(Other definitions for chic that I've seen before include "Elegant and stylishly fashionable" , "Fashionably elegant" , "Elegant and sophisticated" , "Elegantly fashionable" , "cool" .)