through-stone

from The Century Dictionary.

• noun In architecture, a bonder or bond-stone; a stone placed across the breadth of a wall, so that one end appears in each face of the wall, as distinguished from a stone of which the greatest length is placed in the direction of the course of the wall; a perpend. Also thorough-stone.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Scottish and Northern English A horizontal slab acting as a gravestone