Gallinule (7)
I believe the answer is:
moorhen
'gallinule' is the definition.
(I know that moorhen is a type of gallinule)
This is all the clue.
(Other definitions for moorhen that I've seen before include "Bird - hormone (anag)" , "pond bird" , "Water bird" , "Medium-sized, blackish aquatic bird with long toes" , "Black waterbird" .)