The ugly duckling's mother (4)
I believe the answer is:
swan
'the ugly duckling's mother' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swan that I've seen before include "Stately aquatic bird" , "Bird of Cygnus genus" , "possibly mute" , "Large water bird" , "Mute, whooper or Bewick's bird" .)