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

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

“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

"A red line has been crossed", one Gulf official told me.

From BBC • Mar. 16, 2026

“This might be the red line for Saudi that has been crossed,” said Andreas Krieg, a senior lecturer at the School of Security Studies at King’s College London.

From The Wall Street Journal • Mar. 2, 2026

A long wavy red line led the way from the gym to the main office at the far end of the main hallway.

From "Made You Up" by Francesca Zappia