[ il-nis ]
/ ˈɪl nɪs /
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See synonyms for: illness / illnesses on Thesaurus.com

Definition of illness

poor health; sickness: He grew up in an environment known for poverty, illness, and little opportunity for education.
a specific sickness or disease, or an instance of such: Please be as accurate as possible in listing your childhood illnesses.
Obsolete. wickedness.


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Origin of illness

First recorded in 1490–1500; ill + -ness
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does illness mean?

Illness is a state of poor health or sickness, as in I’ve had to miss a lot of work due to illness.

The word illness is also commonly used to refer to a disease or instance of sickness.

This sense of the word is often used when the type of disease is uncertain or unknown or when someone doesn’t want to specify what it is, as in They said that he is in the hospital with an illness, but they didn’t provide any further details. 

The word illness is based on the adjective ill, meaning sick.

Example: The best way to avoid illness is to thoroughly wash your hands.

Where does illness come from?

The first records of the word illness come from around 1500. The suffix -ness is  used to form nouns and indicates a state or condition (in this case, the state of condition of being ill.)

Describing an illness as serious means it could cause serious harm, as in This is a serious illness—not some regular cold. A chronic illness is one that lasts for a long time or frequently recurs. A terminal illness is one that will result in death. The term mental illness refers to a psychological disorder.

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What are some other forms related to illness?

  • illnesses (plural)
  • ill (adjective)

What are some synonyms for illness?

What are some words that share a root or word element with illness

What are some words that often get used in discussing illness?

How is illness used in real life?

Illness is often used in the context of public health, such as in messages about how to fight the spread of illness. It’s also used when someone is sick and doesn’t know why or doesn’t want to say why.



Try using illness!

Is illness used correctly in the following sentence?

The play was postponed because the lead actor was suffering from illness.

How to use illness in a sentence

British Dictionary definitions for illness

/ (ˈɪlnɪs) /

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