Art Deco had endlessly bizarre shapes (9)
I believe the answer is:
octahedra
'shapes' is the definition.
(octahedron is a kind of shape)
'art deco had endlessly bizarre' is the wordplay.
'endlessly' means to remove the last letter.
'bizarre' is an anagram indicator.
'art'+'deco'+'had'='artdecohad'
'artdecohad' with its last letter taken away is 'artdecoha'.
'artdecoha' is an anagram of 'OCTAHEDRA'.
(Other definitions for octahedra that I've seen before include "Eight-sided figures" , "shapes" , "Solid artefacts" , "solids" , "Solid figures with eight plane faces" .)