red line

American  

noun

1. Ice Hockey. a line of the color red that is parallel to and equidistant from the goal lines and divides the rink in half.

2. a limit, point, or boundary beyond which one may not go without incurring negative consequences.

   The use of chemical weapons is a red line, which, if crossed, could trigger military action.

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red line British  

noun

1. a point beyond which a person or group is not prepared to negotiate

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Etymology

Origin of red line

First recorded in 1960–65

Example Sentences

See Examples For:

red line

But the ethical red line would be our stop sign.

From Salon ● Oct. 4, 2026

“We are now dangerously close to crossing a moral red line: the autonomous targeting of humans by machines,” U.N.

From Los Angeles Times ● Aug. 27, 2026

But the PKK leadership has said excluding Ocalan from the legislation would be a red line, warning on Sunday that many of the bill's provisions would remain a "dead letter" if he were not freed.

From Barron's ● Aug. 10, 2026

One red line Meta didn’t cross—barely—was the border into negative free cash flow.

From The Wall Street Journal ● Jul. 30, 2026

If you got four Quarter-Stars, a red line was drawn through the four dots indicating that you had completed your Star.

From "Boy: Tales of a Childhood" by Roald Dahl