Main Page | See live article | Alphabetical index A sinus is a pouch or cavity in any organ or tissue, or an abnormal cavity or passage caused by the destruction of tissue. The term is applied to a large number and variety of structures in the human body, such as a dilated portion of a blood vein, a chronically infected tract such as a fistula, and the air cavities within the cranial bones, especially those located near the nose and connecting to it. These nose-associated sinuses are called paranasal sinuses and are usually what is meant when a person's "sinuses" are referred to. See Also Sinus is a Latin name for the trigonometric function sine, a concept of mathematics. (See trigonometry.) This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.