[ sahy-nuhs ]
/ ˈsaɪ nəs /
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noun, plural si·nus·es.
a curve; bend.
a curving part or recess.
  1. any of various cavities, recesses, or passages, as a hollow in a bone, or a reservoir or channel for venous blood.
  2. one of the hollow cavities in the skull connecting with the nasal cavities.
  3. an expanded area in a canal or tube.
Pathology. a narrow passage leading to an abscess or the like.
Botany. a small, rounded depression between two projecting lobes, as of a leaf.
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Origin of sinus

1590–1600; <Latin sinus (stem sinu-) bent or curved surface, curve, fold


si·nus·like, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use sinus in a sentence

British Dictionary definitions for sinus

/ (ˈsaɪnəs) /

noun plural -nuses
  1. any bodily cavity or hollow space
  2. a large channel for venous blood, esp between the brain and the skull
  3. any of the air cavities in the cranial bones
pathol a passage leading to a cavity containing pus
botany a small rounded notch between two lobes of a leaf, petal, etc
an irregularly shaped cavity

Word Origin for sinus

C16: from Latin: a curve, bay
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for sinus

[ sīnəs ]

A depression or cavity formed by a bending or curving.
A channel for the passage of blood or lymph, without the coats of an ordinary vessel, such as the blood passages in the gravid uterus or in the cerebral meninges.
Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils.
A dilatation in a blood vessel.
A fistula or tract leading to a pus-filled cavity.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for sinus

[ sīnəs ]

A cavity or hollow space in a bone of the skull, especially one that connects with the nose.
A channel for the passage of a body fluid, such as blood.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.