Bird's endlessly stylish (4)
I believe the answer is:
chic
'stylish' is the definition.
('chic' can be similar in meaning to 'stylish')
'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 final letter removed is 'CHIC'.
(Other definitions for chic that I've seen before include "Smart - elegant - fashionable" , "Well turned out" , "Modish" , "Fashionable good taste" , "Elegantly stylish" .)