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

Burchett said his red line is the deployment of ground troops.

From The Wall Street Journal • Apr. 16, 2026

“Territorial integrity is a red line for most Iranians, whether they support the regime or oppose it,” she said.

From The Wall Street Journal • Apr. 3, 2026

Pakistan's president said that this crossed a red line.

From BBC • Mar. 20, 2026

Yet US interest in the vast Arctic territory has not waned, and the red line on the Greenlandic -- and Danish -- side remains the same: any transfer of sovereignty is off the table.

From Barron's • Mar. 10, 2026

Then he draws a red line between the M and the P and hands it to me.

From "Fish in a Tree" by Lynda Mullaly Hunt