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[il-nis] /ˈɪl nɪs/
unhealthy condition; poor health; indisposition; sickness.
Obsolete, wickedness.
1490-1500; ill + -ness
1. ailment, affliction, infirmity. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for illness
  • Yet even when the disease is caused by the same mutation, it can provoke dramatically different degrees of illness.
  • Across the country, people with severe mental illness live what appear to be normal, successful lives.
  • Advanced dementia has often been treated as an amalgamation of symptoms in the aging, rather than a deadly illness in itself.
  • The evidence is mounting: mental illness might be caused by microbes.
  • Severe, chronic mental illness was viewed as relatively rare.
  • The study of human illness depends on bloated rodents.
  • Most suffer from drug or alcohol addiction, mental illness or both.
  • So sometimes the treatment was worse than the original illness.
  • Also features extensive exhibits on the history of the treatment of mental illness.
  • The authors explain that the links between illness and economic loss are complicated.
British Dictionary definitions for illness


a disease or indisposition; sickness
a state of ill health
(obsolete) wickedness
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 illness

"disease, sickness," 1680s, from ill + -ness. Earlier it meant "bad moral quality" (c.1500).

Online Etymology Dictionary, © 2010 Douglas Harper
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illness in Medicine

illness ill·ness (ĭl'nĭs)
Disease of body or mind; poor health; sickness.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Article for illness


a harmful deviation from the normal structural or functional state of an organism. A diseased organism commonly exhibits signs or symptoms indicative of its abnormal state. Thus, the normal condition of an organism must be understood in order to recognize the hallmarks of disease. Nevertheless, a sharp demarcation between disease and health is not always apparent

Learn more about disease with a free trial on
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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