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

See Examples For:

red line

And with nominal yields, real yields, global rates and term premiums all moving in the same direction, a 5.2% yield is now the bright red line investors should watch.

From MarketWatch ● Jul. 24, 2026

If Sorsby’s application is accepted, teams will face a thorny calculus between taking a talented quarterback and casting their lot with a player who crossed the bright red line of betting on his own team.

From The Wall Street Journal ● Jun. 16, 2026

Iran, however, has previously said "zero enrichment" is a red line and a violation of its rights.

From BBC ● Jun. 13, 2026

But Tehran drew a red line on the Dahiyeh, the southern suburbs of Beirut where Hezbollah holds sway.

From Los Angeles Times ● Jun. 10, 2026

While my family’s history of mental illness was cutting through my consciousness like a red line, my scientific work as a cancer biologist was also converging on the normalcy and abnormalcy of genes.

From "The Gene" by Siddhartha Mukherjee