What does "quoin" mean?

Quoin: A wedgelike piece of stone, wood metal, or other material, used for various purposes, as: (a) (Masonry) to support and steady a stone. (b) (Gun.) To support the breech of a cannon. (c) (Print.) To wedge or lock up a form within a chase. (d) (Naut.) To prevent casks from rolling. Hollow quoin. See under Hollow. -- Quoin post (Canals), the post of a lock gate which abuts against the wall.