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

That red line is now being crossed for many other people.

From Salon • Apr. 28, 2026

“Disrupting order and safety in the Strait of Hormuz is considered a red line for Iran,” the Iranian Navy Command said in a statement.

From Los Angeles Times • Apr. 22, 2026

Drawing a red line around using chatbots to generate prose may make it easier to ignore the way that the technology may be shaping writing before one even types a single word.

From Slate • Apr. 17, 2026

Slaughter declined to say which of any of the party's policies would be a red line in negotiations with other parties hoping to lead the next government, but said that housing was a priority.

From BBC • Apr. 7, 2026

The red line on the map had been long.

From "Rowan of Rin" by Emily Rodda