[mon-uh-noo-klee-oh-sis, -nyoo-]

noun Pathology.

the presence of an abnormally large number of mononuclear leukocytes, or monocytes, in the blood.

Origin of mononucleosis

First recorded in 1915–20; mononucle(ar) + -osis Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for mononucleosis

EBV, mononucleosis

British Dictionary definitions for mononucleosis



pathol the presence of a large number of monocytes in the blood
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 mononucleosis

1920, coined from mononuclear + Modern Latin -osis "abnormal condition."

Online Etymology Dictionary, © 2010 Douglas Harper

mononucleosis in Medicine




Abnormally large numbers of mononuclear white blood cells in the blood, especially forms that are not normal.
Infectious mononucleosis.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

mononucleosis in Science



A common infectious disease usually affecting young people, caused by the Epstein-Barr virus and characterized by fever, sore throat, swollen lymph nodes, and fatigue. The symptoms may last for several weeks.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

mononucleosis in Culture



An acute and infectious disease caused by a virus; its symptoms include fever, swelling of the lymph nodes, and general exhaustion. Mononucleosis gets its name from the kind of white blood cell (monocyte) that increases in number in the blood of persons who have the disease. There is no specific treatment, but sufferers usually recover within a few weeks.


Mononucleosis is sometimes called the “kissing disease,” because at one time the virus was thought to be transmitted by kissing. The virus can be found in the saliva of those who have the disease, so there may be some truth in the belief.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.