Sinus
Sinus may refer to:

Anatomy
Sinus (anatomy), a sac or cavity in any organ or tissue
Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including:
Maxillary sinus, is the largest of the paranasal sinuses, under the eyes, in the maxillary bones
Frontal sinus, superior to the eyes, in the frontal bone, which forms the hard part of the forehead
Ethmoid sinus, formed from several discrete air cells within the ethmoid bone between the eyes and under the nose
Sphenoidal sinus, in the sphenoid bone at the center of the skull base under the pituitary gland
Anal sinuses, the furrows which separate the columns in the rectum
Dural venous sinuses, venous channels found between layers of dura mater in the brain
Sinus (botany), a space or indentation, usually on a leaf

Heart
Sinus node, a structure in the superior part of the right atrium
Sinus rhythm, normal beating on an ECG
Coronary sinus, a vein collecting blood from the heart
Sinus venosus, a cavity in the heart of embryos
Sinus venarum, a part of the wall of the right atrium in adults, developed from the sinus venosus

Other uses
Sinus (Chalcidice), a town of ancient Chalcidice, Greece
Sinus, gulf or bay in Latin, used in numerous toponyms in ancient writing (e.g., Sinus Magnus, Sinus Flanaticus, etc.)
Sine, a trigonometric math function (Latin sinus)

See also
Sinus Medii, a small lunar mare
Sinus Successus, a lunar feature
Sines, a municipality in Alentejo, Portugal (Latin Sinus)
Sinusitis, a common ailment resulting in the inflammation of the paranasal sinuses