Design a long coat shaped like an umbrella? (9)
I believe the answer is:
octagonal
'shaped like an umbrella?' is the definition.
(umbrellas typically have eight segments)
'design a long coat' is the wordplay.
'design' indicates anagramming the letters.
'a'+'long'+'coat'='alongcoat'
'alongcoat' anagrammed gives 'OCTAGONAL'.
(Other definitions for octagonal that I've seen before include "Having eight straight sides" , "With eight sides and angles" , "Eight-sided" , "Eight sided" , "Having eight sides as in geometric figure" .)