red line
Americannoun
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Ice Hockey. a line of the color red that is parallel to and equidistant from the goal lines and divides the rink in half.
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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.
noun
Etymology
Origin of red line
First recorded in 1960–65
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Iran, however, has previously said "zero enrichment" is a red line and a violation of its rights.
From BBC • Jun. 13, 2026
He could not stay within the one red line that the court drew for him.
From Slate • Jun. 1, 2026
The finance ministry said that even the title of the work area -- "environmental impact of digital technology" -- had proved a "red line" for the American side.
From Barron's • May 29, 2026
The attacks on national infrastructure were a red line for both the U.A.E. and Saudi Arabia.
From The Wall Street Journal • May 16, 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
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
