on·​set | \ ˈȯn-ˌset How to pronounce onset (audio) , ˈän-\

Definition of onset

1 : attack, assault withstand the onset of the army
2 : beginning, commencement the onset of winter the onset of age-related diseases

Keep scrolling for more

Examples of onset in a Sentence

the walls withstood the onset of the first battalion the claim that if you take enough vitamin C at the onset of a cold, you'll often recover faster

Recent Examples on the Web

This isn't the first study to find earlier onset of puberty in boys. Minali Nigam, CNN, "Boys are hitting puberty earlier, partially due to rise in BMI, study suggests," 22 July 2019 Among the 35 players without CTE in the study, those who played football before age 12 had an earlier onset of cognitive symptoms by an average of 20 years, and behavior and mood symptoms by 22 years. Sean Gregory, Time, "Playing Youth Tackle Football Is Linked to Earlier Symptoms of Brain Disease," 30 Apr. 2018 Flu often has an abrupt onset with fever, cough and body aches. Jeanne Houck, Cincinnati.com, "Cincinnati Children's Hospital expert on what to do to protect your family from the flu," 23 Jan. 2018 Learn the early onset of symptoms of mental illness, available treatments, gain insight into the daily experience of living with mental illness and dispel common misconceptions about the illness. Linda Mcintosh, sandiegouniontribune.com, "Fundraiser set for teen fighting cancer ...plus more in the community," 17 Jan. 2018 Singh hopes that her tech could one day help doctors using telemedicine identify the early onset of conditions like Parkinson’s disease. Jennifer Alsever, Fortune, "Forget Face ID. The Future of Secure Authentication Is Your Voice," 6 Jan. 2018 Health officials in Indiana, Illinois, Oregon and Minnesota have also reported fatalities from sudden-onset illnesses that officials linked to vaping. Anchorage Daily News, "California man is seventh person to die from suspected vape-related illness," 17 Sep. 2019 That same month, doctors reported the first case of a sudden-onset, severe lung illness associated with vaping. Katherine Ellen Foley, Quartz, "Is it safe to vape?," 9 Sep. 2019 The worst long-term effect of excessive heat exposure would be death by heatstroke (especially from late-onset multi-organ failure and skin necrosis/slough that are secondary to heatstroke)! Maddie Hiatt, House Beautiful, "How To Keep Your Pet Safe This Summer," 26 July 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'onset.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of onset

circa 1522, in the meaning defined at sense 1

Keep scrolling for more

Learn More about onset

Statistics for onset

Last Updated

7 Oct 2019

Look-up Popularity

Time Traveler for onset

The first known use of onset was circa 1522

See more words from the same year

Keep scrolling for more

More Definitions for onset



English Language Learners Definition of onset

: the beginning of something


on·​set | \ ˈȯn-ˌset How to pronounce onset (audio) , ˈän-\

Kids Definition of onset

1 : beginning sense 1 the onset of winter


on·​set | \ ˈȯn-ˌset, ˈän- How to pronounce onset (audio) \

Medical Definition of onset

: the initial existence or symptoms of a disease the onset of scarlet fever

Keep scrolling for more

More from Merriam-Webster on onset

Rhyming Dictionary: Words that rhyme with onset

Thesaurus: All synonyms and antonyms for onset

Spanish Central: Translation of onset

Nglish: Translation of onset for Spanish Speakers

Britannica English: Translation of onset for Arabic Speakers

Comments on onset

What made you want to look up onset? Please tell us where you read or heard it (including the quote, if possible).


suitable to be imparted to the public

Get Word of the Day daily email!

Test Your Vocabulary

Where in the World? A Quiz

  • peter bruegel tower of babel painting
  • What language does pajama come from?
Name That Thing

Test your visual vocabulary with our 10-question challenge!


Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!