Bird that won't fly in still weather (4)
I believe the answer is:
kite
This clue could be a double definition.
'bird that won't' is the first definition.
'kite' can be an answer for 'bird' (kite is a kind of bird). I'm not sure about the rest of the definition.
'fly in still weather' is the second definition.
'kite' can be an answer for 'fly' (thesaurus). I'm not certain of the 'in still weather' bit.
Can you help me to learn more?
(Other definitions for kite that I've seen before include "Toy; aircraft (dated)" , "Small hawk" , "Winger" , "Toy that flies on end of string" , "Quadrilateral; bird" .)