Shaped like some open umbrellas (9)
I believe the answer is:
octagonal
'shaped like some open umbrellas' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for octagonal that I've seen before include "with certain sides" , "In unusual shape" , "With many sides" , "With eight sides and angles" , "Eight-sided" .)