noun, plural sinuses.
a curve; bend.
a curving part or recess.
any of various cavities, recesses, or passages, as a hollow in a bone, or a reservoir or channel for venous blood.
one of the hollow cavities in the skull connecting with the nasal cavities.
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.

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

sinuslike, adjective Unabridged


Sinus, Sinus Iridum. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
sinus (ˈsaɪnəs)
n , pl -nuses
1.  anatomy
 a.  any bodily cavity or hollow space
 b.  a large channel for venous blood, esp between the brain and the skull
 c.  any of the air cavities in the cranial bones
2.  pathol a passage leading to a cavity containing pus
3.  botany a small rounded notch between two lobes of a leaf, petal, etc
4.  an irregularly shaped cavity
[C16: from Latin: a curve, bay]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1597, "abscess, sore," from M.L. sinus, from L. sinus "bend, fold, curve." Meaning "hollow curve or cavity in the body" is attested from 1672. Sinusitis "inflammation of a sinus" is recorded from 1896.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

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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American Heritage
Science Dictionary
sinus   (sī'nəs)  Pronunciation Key 

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  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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Example sentences
She used to grind her teeth constantly due to painful sinus and ear infections
  linked to her condition.
So far, they've done virtual practice sessions with their prototype on several
  patients about to undergo sinus surgery.
Heck, it isn't even ingrown toenails and sinus infections.
Wondering why my cold and sinus combo meds aren't clearing my sinuses.
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