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[sahy-nuh s] /ˈsaɪ nəs/
noun, plural sinuses.
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 forms
sinuslike, adjective


[ir-i-duh m] /ˈɪr ɪ dəm/
Sinus, Sinus Iridum. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for sinus


noun (pl) -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
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
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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
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sinus in Medicine

sinus si·nus (sī'nəs)

  1. A depression or cavity formed by a bending or curving.

  2. 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.

  3. Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils.

  4. A dilatation in a blood vessel.

  5. 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.
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sinus in Science

  1. A cavity or hollow space in a bone of the skull, especially one that connects with the nose.

  2. A channel for the passage of a body fluid, such as blood.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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