Amorphous mass (4)
I believe the answer is:
blob
'amorphous mass' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for blob that I've seen before include "Drop of thick liquid or viscous substance" , "Small piece signifying nothing" , "Indeterminate mass" , "Indistinct shape" , "Indeterminate drop of liquid" .)