Definition of sinus in US English:



  • 1often sinusesZoology Anatomy
    A cavity within a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities.

    • ‘During a physical examination, your doctor may feel for tenderness in the area of the sinuses and examine your nasal passages looking for inflammation, secretions or deformities.’
    • ‘The two cavernous sinuses are large veins lying within the skull cavity, immediately behind each eye socket and on either side of the pituitary gland.’
    • ‘Common wood dust produced in sanding furniture and cabinets is associated with increases in cancer of the nasal cavities and sinuses.’
    • ‘The sheep's nasal cavity and sinuses are orientated in a similar fashion to man's.’
    • ‘Your sinuses are hollow spaces within the bones of your face, behind and above your nose.’
    space, chamber, hollow, hole, pocket, pouch
    View synonyms
    1. 1.1 An irregular venous or lymphatic cavity, reservoir, or dilated vessel.
    2. 1.2Medicine An infected tract leading from a deep-seated infection and discharging pus to the surface.
      • ‘Pneumonia, bronchitis, and sinus and ear infections are three examples of complications from flu.’
      • ‘Sinusitis is when the sinuses get infected or irritated and cannot drain mucus as well as they should.’
      • ‘The paranasal sinuses are a common infection site in children and adolescents.’
      • ‘When the linings of your sinuses become infected, usually due to viruses or bacteria, they may swell, causing an obstruction and interfering with the normal drainage of mucus.’
      • ‘Asthma, allergies, or a chronic infection in the sinuses or breathing passages might also be responsible for long-term coughs.’
    3. 1.3Botany A rounded notch between two lobes on the margin of a leaf or petal.
  • 2Physiology
    as modifier Relating to or denoting the sinoatrial node of the heart or its function as a pacemaker.

    ‘sinus rhythm’
    ‘sinus tachycardia’
    • ‘The sinus node can increase your heart rate during times of high demand, such as during exercise.’
    • ‘Sinus dysrhythmia refers to a malfunction of the sinus node, the heart's natural pacemaker.’
    • ‘A normal heart rhythm is one in which each heartbeat originates in the sinus node and proceeds normally through the rest of the body's electric conduction system.’
    • ‘Although this medicine has been used to treat heart failure for more than 200 years, its role in patients with congestive heart failure and sinus rhythm is still debatable.’
    • ‘Electrodes positioned at various sites in the heart can give only limited data about intracardiac conduction during sinus rhythm at rest.’


Late Middle English (in the medical sense): from Latin, literally ‘a recess, bend’.