The term sinus is used to denote a variety of spaces and passages in the body. Thus, there are the spaces in certain bones,the frontal sinus, the sphenoidal sinus and so on, and the large venous channels in the membranes of the brain, the superior longitudinal sinus, the lateral sinus and other such sinuses. The ventricle of the larynx is known also as the sinus of the larynx, and certain other cavities are also called sinuses. Lastly, a narrow suppurating tract is called a sinus. See: Abscess.. Colds.. Flu.. Nose..