Leech - The aft (back) edge of a fore-and-aft sail is called the leech (also spelled leach), which is opposite the luff, and on a triangular sail forms the hypotenuse of the triangle[REF] The leech is either side edge of a symmetrical sail.
Roach is a term also applied to square sail design-it is the arc of a circle above a straight line from clew to clew at the foot of a square sail, from which sail material is omitted.