The Collaborative International Dictionary
perbend
Perpender \Per*pend"er\, n. [F. parpaing, pierre parpaigne; of uncertain origin.] (Masonry) A large stone reaching through a wall so as to appear on both sides of it, and acting as a binder; -- called also perbend, perpend stone, and perpent stone.
Wiktionary
perbend
n. (alternative form of perpender English)