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

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

From BBC • Mar. 20, 2026

Pahlavi accused them of threatening national unity and said "Iran's territorial integrity is the ultimate red line."

From Barron's • Mar. 5, 2026

“We think it is premature to expect $100/bbl as an important red line has yet to be crossed,” it says.

From The Wall Street Journal • Mar. 2, 2026

Then I hold the compass to my belly button, get the red line to match up with north, and follow that through the charred remnants of Rockledge Park until I hit the firebreak.

From "Wayward Creatures" by Dayna Lorentz