Oh dear, cat wrecked geometrical shapes! (9)
I believe the answer is:
octahedra
'geometrical shapes' is the definition.
'octahedra' can be an answer for 'shapes' (octahedron is a kind of shape). I am not sure about the 'geometrical' bit.
'oh dear cat wrecked' is the wordplay.
'wrecked' is an anagram indicator.
'oh'+'dear'+'cat'='ohdearcat'
'ohdearcat' is an anagram of 'OCTAHEDRA'.
Can you help me to learn more?
(Other definitions for octahedra that I've seen before include "things with many faces" , "Eight-sided figures" , "solid objects" , "shapes" , "solids" .)