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

Now Mexico’s leaders are drawing a red line.

From The Wall Street Journal • Jun. 6, 2026

Xi and Trump steered away from publicly discussing "geopolitical minefields" such as Taiwan -- long considered in China as a "red line" and a core interest -- and other human rights issues, Lim said.

From Barron's • May 15, 2026

The population is expected to grow by 1.7 million in the 10 years after 2024 as shown by the dotted red line in the graph above.

From BBC • 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

A fine red line of a scar marked Angela's check, but she looked content and lovely as ever in her pale blue bridesmaid's gown.

From "The Westing Game" by Ellen Raskin