A triangular sail, extended by a long yard, which is slung at about one fourth of its length from the lower end, to a low mast, this end being brought down at the tack, while the other end is elevated at an angle or about forty-five degrees; -- used in small boats, feluccas, xebecs, etc., especially in the Mediterranean and adjacent waters. Some lateen sails have also a boom on the lower side.  [1913 Webster]