Wee creature (6)
I believe the answer is:
amoeba
'wee creature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amoeba that I've seen before include "Water protozoan" , "Freshwater or marine protozoa" , "Microscopic, single-cell creature" , "Single-celled form of life of ever-changing shape" , "Protozoan life form" .)