The Collaborative International Dictionary
Backjoint
Backjoint \Back"joint`\ (b[a^]k"joint`), n. [Back, a. or adv. + joint.] (Arch.) A rebate or chase in masonry left to receive a permanent slab or other filling.
Wiktionary
backjoint
n. (context architecture English) A rebate or chase in masonry left to receive a permanent slab or other filling.