See Pituitary body, under Pituitary.
Greek hypo = down, physis = growth, hence, a downgrowth (from the brain). However, this is not the whole truth. Part is an upgrowth from the pharynx, adjective - hypophysial.
the master gland of the endocrine system; located at the base of the brain
(Gr. under growth): Endocrine gland (pituitary) which occupis the hypophysial fossa of the sphenoid bone. It is attached to the base of the brain (hypothalamus) by the infundibular stalk and consists of the adenohypophysial and neurohypophysial lobes, both of which are under neural control.