Sounding like a bird, not half quaint (4)
I believe the answer is:
twee
'quaint' is the definition.
(I've seen this before)
'sounding like a bird not half' is the wordplay.
'sounding like a bird' becomes 'tweeting'.
'not half' means to take half the letters.
'tweeting' halved is 'TWEE'.
(Other definitions for twee that I've seen before include "Sentimentally pretty" , "Overly sentimental or pretty" , "Affectedly dainty or quaint" , "Affectedly dainty or refined" , "Precious - sentimental" .)