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

But most of them now see attacks on energy infrastructure as a red line.

From BBC • Apr. 6, 2026

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

From BBC • Mar. 20, 2026

This is seemingly a red line for Anthropic, which doesn’t want its products used for autonomous weapons or mass surveillance.

From The Wall Street Journal • Mar. 11, 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

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