Real Dictionary

cerebellum
one of the major divisions of the vertebrate brain, situated in humans above the medulla oblongata and beneath the cerebrum, whose function is coordination of voluntary movements and maintenance of bodily equilibrium [...]
The cerebellum is a part of the brain in humans and other mammals that controls the body's movements and balance.
the outer layer of any organ or part, such as the grey matter in the brain that covers the cerebrum (cerebral cortex) or the outer part of the kidney ( renal cortex) [...]

cerebellum in American English
the section of the brain behind and below the cerebrum: it consists of two lateral lobes and a middle lobe, and functions as the coordinating center for muscular movement
noun: a large portion of the brain, serving to coordinate voluntary movements, posture, and balance in humans, being in back of and below the cerebrum and consisting of two lateral lobes and a central lobe

cerebellum in British English
noun: one of the major divisions of the vertebrate brain, situated in humans above the medulla oblongata and beneath the cerebrum, whose function is coordination of voluntary movements and maintenance of bodily equilibrium