quoin

"Knock away the quoin, entirely;" he said to the captain of the gun, when he had got the range; "now mind her when she lifts, forward; keep the ship steady, Sir—fire!"

From The Water-Witch or, the Skimmer of the Seas by James Fenimore Cooper

So that below the girdle, we find twenty-five facets: 8 cross, 8 skill, 4 pavilion, 4 quoin, and 1 collet.

From The Chemistry, Properties and Tests of Precious Stones by John Mastin

Back's Inlet presents on each side a succession of lofty precipitous headlands, which have the shape termed, by seamen, "the gunner's quoin."

From Narrative of a Second Expedition to the Shores of the Polar Sea by John Franklin

I should have liked to see you when you were making for the side all top-heavy, and went flying over after the great quoin as you called it.

From Fitz the Filibuster by Harold Piffard

The piece of wood between the cheeks or brackets which, with the intervention of the quoin, supports the breech of the gun.

From The Sailor's Word-Book An Alphabetical Digest of Nautical Terms, including Some More Especially Military and Scientific, but Useful to Seamen; as well as Archaisms of Early Voyagers, etc. by Sir Edward Belcher