Thesaurus.com
Dictionary.com
Definitions

illness

[il-nis] / ˈɪl nɪs /
NOUN
disease; bad health
Synonyms
STRONGEST
ailment breakdown collapse disability disorder disturbance flu ill health malady relapse seizure sickness syndrome virus
STRONG
affliction attack bug complaint confinement convalescence dose fit indisposition infirmity malaise prostration
WEAK
ailing diseasedness failing health poor health unhealth what's going around
Antonyms
STRONGEST
health order
STRONG
aid good health healthiness
WEAK
well-being wellness

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

The musician's death on Sunday came after a short illness, the choral group posted on their Facebook page.

From BBC • Apr. 6, 2026

Both bots identified dips in my heart-rate variability data and an increase in resting heart rate from my smartwatch, which could indicate my body has been fighting an illness.

From The Wall Street Journal • Apr. 4, 2026

Patients with more severe illness had a greater number of these clusters, while healthy donor lungs showed none.

From Science Daily • Apr. 3, 2026

Older adults are far more likely to develop severe illness from flu or COVID, and new research from UC San Francisco offers an explanation.

From Science Daily • Apr. 3, 2026

In high enough doses, radiation sickness almost always causes nausea, headaches, and a general feeling of illness that can last anywhere from a few hours to two days.

From "Meltdown" by Deirdre Langeland

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.