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sinus,cavity or hollow space in the body, usually filled with air or blood. In humans the paranasal sinuses, mucus-lined cavities in the bones of the face, are connected by passageways to the nose and probably help to warm and moisten inhaled air. When drainage from them is blocked, as after a cold, these sinuses often become infected, a condition called sinusitis. The accumulation of pus results in pressure, headaches, pain, and general discomfort. In invertebrates one of the spaces among the muscles and viscera through which blood returns to the heart is also known as a sinus.
sinus(sÿ -nŭs) A semienclosed break along the borders of a lunar mare or in a scarp. The word is used in the approved name of such a feature on the Moon. (Latin: bay)
in anatomy, a cavity, protrusion, or long closed channel. In vertebrates (including man), the term “sinus” refers to a channel filled with venous blood in the dura mater. The cavity in some cranial bones is also called a sinus. [23–1297–]
A cavity, recess, or depression in an organ, tissue, or other part of an animal body.
a. any bodily cavity or hollow space
b. a large channel for venous blood, esp between the brain and the skull
c. any of the air cavities in the cranial bones
2. Pathol a passage leading to a cavity containing pus
3. Botany a small rounded notch between two lobes of a leaf, petal, etc.
4. an irregularly shaped cavity