Definitions for "Rhombencephalon"
The most caudal of the primary vesicles that are present in the early neural tube, which later gives rise to two secondary vesicles: metencephalon (prospective pons and cerebellum) and myelencephalon (prospective medulla oblongata).
(Greek rhombos = rhomboid, enkephalos = brain) hindbrain, at the early (3 primary vesicle) stage of brain development, this is the most caudal vesicle. At the 5 secondary vesicle stage of brain development this then forms both the metencephalon and the myeloncephalon. Finally forming the adult structures of cerebellum, pons and medulla. (More? Neural Notes)
the posterior portion of the brain including cerebellum and brainstem