Quoin \Quoin\, n. [See Coin, and cf. Coigne.]

1. (Arch.) Originally, a solid exterior angle, as of a building; now, commonly, one of the selected pieces of material by which the corner is marked.

Note: In stone, the quoins consist of blocks larger than those used in the rest of the building, and cut to dimension. In brickwork, quoins consist of groups or masses of brick laid together, and in a certain imitation of quoins of stone.

Source: Webster's Revised Unabridged Dictionary (1913)