[sahy-nuh s]

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.

Origin of sinus

1590–1600; < Latin sinus (stem sinu-) bent or curved surface, curve, fold
Related formssi·nus·like, adjective


[ir-i-duh m]


Sinus. Sinus Iridum. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for sinus

recess, opening, hollow, pocket, channel, depression, antrum

Examples from the Web for sinus

Contemporary Examples of sinus

Historical Examples of sinus

British Dictionary definitions for sinus


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

Word Origin and History for sinus

"hollow curve or cavity in the body," early 15c., from Medieval Latin sinus, from Latin sinus "bend, fold, curve, a bent surface; a bay, bight, gulf; a fold in land;" also "fold of the toga about the breast," hence "bosom," and figuratively "love, affection, intimacy; interior, inmost part;" of unknown origin.

Online Etymology Dictionary, © 2010 Douglas Harper

sinus in Medicine




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.

sinus in Science



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.