Type of duck (5)
I believe the answer is:
eider
'type of duck' is the definition.
(I know that Eider is a type of sea duck)
This is all the clue.
(Other definitions for eider that I've seen before include "Down comes from this" , "Source of fine soft down" , "Reed I turn into a duck" , "Duck valued for its fine soft down" , "Species of duck" .)