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Synonyms

be on

Idioms  

  1. Be taking medication or an illegal drug, as in Are you on some antibiotic? or He was definitely on narcotics when it happened . [1930s]

  2. Be in favor of something or willing to participate, as in We're going dancing after the play—are you on? [ Colloquial ; late 1800s]

  3. Be engaged in some action, especially on the stage, as in Hurry up, you're on in five minutes . [Late 1700s]

  4. Perform extremely well, as in I can't return Dan's serve—he's really on today . [ Slang ; second half of 1900s]

  5. Be scheduled, as in Is tonight's rally still on? [ Colloquial ; second half of 1990s]

  6. be on one . Be at one's expense, either as a treat or the butt of a joke. For example, This round of drinks is on me , or He enjoys a good laugh, even when the joke's on him . [ Colloquial ; second half of 1800s]

  7. not be on . Be unacceptable, not allowable, as in I can't believe you'd cancel; that's just not on . This usage is more common in Britain than America. [ Colloquial ; 1930s] For a synonym, see not done . Also see be on to .

  8. see be on.

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.

Larry Ellison predicts an AI-powered surveillance state in which “citizens will be on their best behavior, because we’re constantly recording and reporting everything that is going on.”

From The Wall Street Journal • Apr. 2, 2026

Intel investors have been reacting positively to its recent announcement of a change to a joint-venture arrangement — and another a similar catalyst may be on the horizon.

From MarketWatch • Apr. 2, 2026

The King will be on a different coast but will be in the same country where his son Prince Harry and daughter-in-law Meghan now live.

From BBC • Mar. 31, 2026

And the more flexible you can be on the timing or destination, the better chance you’ll have at finding deals.

From Los Angeles Times • Mar. 31, 2026

“Hey, that’s a good theory. You might be on to something!”

From "The Bletchley Riddle" by Ruta Sepetys and Steve Sheinkin

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.