(nautical) A triangular fore-and-aft sail set on a boom in such way that the tack is attached to the hull of the vessel and the free end of the boom lifts the sail.
1995, George F. Hourani, John Carswell, Arab Seafaring in the Indian Ocean in Ancient and Early Medieval Times, Princeton University Press, Expanded Edition, page 103,
The mere fact that this type of lateen no longer exists in the Mediterranean proves nothing; it is always possible that it might have originated there and later given way there to the still superior triangular form. But there are more substantial reasons for believing that the lateen came from the Indian Ocean to the Mediterranean. The earliest evidence of the existence of lateens in the Mediterranean is in Greek Byzantine manuscripts of the late ninth century, which show drawings of lateens (Plates 5 and 6).