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definitions

sinusitis

[sahy-nuh-sahy-tis]
noun Pathology.
  1. inflammation of a sinus or the sinuses.

Origin of sinusitis

From New Latin, dating back to 1900–05; see origin at sinus, -itis
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for sinusitis

sinusitis

noun
  1. inflammation of the membrane lining a sinus, esp a nasal sinus
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 sinusitis
n.

"inflammation of the sinuses," 1896; see sinus + -itis.

Online Etymology Dictionary, © 2010 Douglas Harper
sinusitis in Medicine

sinusitis

[sī′nə-sī′tĭs]
n.
  1. Inflammation of the mucous membrane of a sinus, especially of the paranasal sinuses.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.