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
The term "chemical cosh"
The term "chemical cosh" (a club) is sometimes used popularly for a strong sedative, particularly for:

widespread dispensation of antipsychotic drugs in residential care to make people with dementia easier to manage. use of methylphenidate to calm children with attention deficit hyperactivity disorder, though paradoxically this drug is known to be a stimulant. See also Antipsychotic controversy

Types of sedatives
Therapeutic use
Doctors and veterinarians often administer sedatives to patients in order to dull the patients anxiety related to painful or anxiety-provoking procedures. Although sedatives do not relieve pain in themselves, they can be a useful adjunct to analgesics in preparing patients for surgery, and are commonly given to patients before they are anaesthetized, or before other highly uncomfortable and  invasive procedures like cardiac catheterization, colonoscopy or MRI. Risks
Sedative dependence
Some sedatives can cause psychological and physical dependence when taken regularly over a period of time, even at therapeutic doses. Dependent users may get withdrawal symptoms ranging from restlessness and insomnia to convulsions and death. When users become psychologically dependent, they feel as if they need the drug to function, although physical dependence does not necessarily occur, particularly with a short course of use. In both types of dependences, finding and using the sedative becomes the focus in life. Both physical and psychological dependence can be treated with therapy. Misuse
Many sedatives can be misused, but barbiturates and benzodiazepines are responsible for most of the problems with sedative use due to their widespread recreational or non-medical use.