1. a suffix occurring in nouns that denote actions, conditions, or states (hypnosis; leukocytosis; osmosis), especially disorders or abnormal states (chlorosis; neurofibromatosis; tuberculosis).
Compare -otic.

Origin of -osis

on the model of Greek borrowings ending in Greek -ōsis, as sklērōsis sclerosis, derived orig. from verbs ending in the formative -o- (-ō- in noun derivatives), with the suffix -sis -sis
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for -osis


suffix forming nouns
  1. indicating a process or statemetamorphosis
  2. indicating a diseased conditiontuberculosis Compare -iasis
  3. indicating the formation or development of somethingfibrosis

Word Origin for -osis

from Greek, suffix used to form nouns from verbs with infinitives in -oein or -oun
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 -osis

word-forming element expressing state or condition, in medical terminology denoting "a state of disease," from Latin -osis and directly from Greek -osis, formed from the aorist of verbs ending in -o. It corresponds to Latin -atio.

Online Etymology Dictionary, © 2010 Douglas Harper

-osis in Medicine


  1. Condition; process; action:osmosis.
  2. Diseased or abnormal condition:proptosis.
  3. Increase; formation:leukocytosis.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

-osis in Science


  1. A suffix that means:
  2. Diseased condition, as in tuberculosis.
  3. Condition or process, as in osmosis.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.