Bluish green — duck (4)
I believe the answer is:
teal
This clue is a double definition.
'bluish green' is the first definition.
(I know that bluish green can be written as teal)
'duck' is the second definition.
(I know that teal is a type of duck)
(Other definitions for teal that I've seen before include "Small river duck" , "Raise (subject matter)" , "Dark greenish-blue colour" , "Dark green-blue; duck" , "Variety of small ducks" .)