Amorphous shape (4)
I believe the answer is:
blob
'amorphous shape' is the definition.
(blob is a kind of amorphous shape)
This is all the clue.
(Other definitions for blob that I've seen before include "Drop of thick liquid or viscous substance" , "Indistinct object" , "Something small, soft and round" , "Small piece signifying nothing" , "Mark signifying nothing" .)