Small chicken hat made of straw (7)
I believe the answer is:
leghorn
I believe this is a double definition.
'small chicken' is the first definition.
(small breed of chicken)
'hat made of straw' is the second definition.
(type of straw hat)
(Other definitions for leghorn that I've seen before include "port" , "Breed of chicken" , "Breed of domestic foul" , "Chicken; straw hat" .)