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

Danish and Greenlandic officials have pushed back strongly against giving up any form of ownership, and repeatedly stated that sovereignty is a "red line".

From BBC

"We have some red lines... We have to respect our territorial integrity. We have to respect international law, sovereignty."

From Barron's

Europeans viewed the threat as a red line requiring a much more forceful response than against the president’s tariff moves last year because it challenged a country’s sovereignty.

From The Wall Street Journal

You may have certain red lines, like no main road or no north-facing back garden.

From MarketWatch

"We withdrew to predominantly Kurdish areas and protecting them is a red line," he added.

From BBC