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Be taking medication or an illegal drug, as in
Are you on some antibiotic?
He was definitely on narcotics when it happened
Be in favor of something or willing to participate, as in
We're going dancing after the play—are you on?
; late 1800s
Be engaged in some action, especially on the stage, as in
Hurry up, you're on in five minutes
Perform extremely well, as in
I can't return Dan's serve—he's really on today
; second half of 1900s
Be scheduled, as in
Is tonight's rally still on?
; second half of 1990s
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
He enjoys a good laugh, even when the joke's on him
; second half of 1800s
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.
For a synonym, see
be on to
The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Nearby words for be on
be in the weeds
be in the zone
be my guest
be on it
be on someone's case
be on the lookout
be on to
be one's own person