Gent hailing smashing bird (11)
I believe the answer is:
nightingale
'bird' is the definition.
(nightingale is a kind of bird)
'gent hailing smashing' is the wordplay.
'smashing' is an anagram indicator.
'gent'+'hailing'='genthailing'
'genthailing' anagrammed gives 'NIGHTINGALE'.
(Other definitions for nightingale that I've seen before include "See 17" , "Singer in London square" , "Woman of note" , "Migratory songbird" , "Small thrush with a melodious song" .)