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• 9/11
  9/11

  September 11, 2001: the day on which Islamic terrorists, believed to be part of the Al-Qaeda network, hijacked four commercial airplanes and crashed two of them into the World Trade Center in New York City and a third one into the Pentagon in Virginia: the fourth plane crashed into a field in rural Pennsylvania.
• 9-11
  9-11

  See September 11 attacks.

9/11

American  

[nahyn-i-lev-uhn] / ˈnaɪn ɪˈlɛv ən /

Or 9-11

1. September 11, 2001: the day on which Islamic terrorists, believed to be part of the Al-Qaeda network, hijacked four commercial airplanes and crashed two of them into the World Trade Center in New York City and a third one into the Pentagon in Virginia: the fourth plane crashed into a field in rural Pennsylvania.

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9-11 Cultural  

1. See September 11 attacks.

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Etymology

Origin of 9/11

First recorded in 2000–05

Example Sentences

After 9/11, the government punished ordinary Muslim Americans who refused its overtures to spy, at great personal cost, for it.

From Slate • May 26, 2026

In World War II we fought fascism; in the Cold War we opposed communism; and after 9/11 we rallied around the war on terror.

From The Wall Street Journal • May 19, 2026

Think about it: When “Battlestar Galactica” was introduced as a miniseries in 2003, America was still reeling from 9/11.

From Salon • May 5, 2026

Giuliani became known as "America's Mayor" after leading New York City through the aftermath of the 9/11 attacks.

From BBC • May 3, 2026

He’d assign us reports where we reimagined periods of significant deaths—the plague, the world wars, 9/11, et cetera—and how people would’ve behaved had Death-Cast been around to deliver the warning.

From "They Both Die at the End" by Adam Silvera