By Bob Diamond
Leech seems like a peculiar word to name a part of a sail but it makes sense if you go back far enough into sailing history. Going back to the late 1700's and early 1800's is far enough. That’s when trade and warfare was conducted on square-rigged ships. These plied the trade winds, which largely meant sailing east or west. In those days time was measured exclusively in accordance with the sun. When the sun was at its highest above the horizon, noon was declared and the watch was changed. This is also when the rum rations were given out. (A lot more drinking was done in those days.)
A little about square-rig terminology: The spars that hold up the square sails from the top are called yards. At each end of the yard is the yardarm, the part of the yard that sticks out beyond the edge of the square sail. While sailing, each yardarm can be defined as either the windward or leeward yardarm depending on the tack being sailed. Each side of the sail is also described as either windward or leeward.
Sailors who have spent a lot of time in harbor bars may have heard the phrase, "The sun is over the yardarm." In its modern context this means its time to drink. Originally it just meant that it was high noon since that's where the sun could be observed if the ship was sailing directly east or west.
Getting back to square sail terminology, we have the windward edge and the leeward or lee edge of the sail. Anyway, you can see that after drinking all that rum it wouldn't take much time for the term "lee edge" to be corrupted to "leech". The luff and leech of a fore-and-aft sail function much the same way as they do in a square sail, which is why we call the leech the leech to this day.