Merriam-Webster Collegiate Dictionary - parietal

 I. adjective  Etymology: Middle English, from Medieval Latin ~is, from pariet-, paries wall of a cavity or hollow organ, from Latin, wall  Date: 15th century  1.  a. of or relating to the walls of a part or cavity  b. of, relating to, or forming the upper posterior wall of the head  2. attached to the main wall rather than the axis or a cross wall of a plant ovary — used of an ovule or a placenta  3. of or relating to college living or its regulation; especially of or relating to ~s  II. noun  Date: 15th century  1. a ~ part (as a bone, scale, or plate)  2. plural the regulations governing the visiting privileges of members of the opposite sex in campus dormitories