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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

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

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

From Salon • May 5, 2026

Charles and Camilla paid their respects at the 9/11 Memorial and met locals including Mayor Zohran Mamdani, a get-together that came just hours after the couple were hosted by President Trump.

From The Wall Street Journal • Apr. 30, 2026

The importance of the 9/11 attacks had been raised by King Charles in his speech to the US Congress on Tuesday.

From BBC • Apr. 29, 2026

“On 9/11, my family doesn’t leave the house much. Not unless we have to.”

From "Towers Falling" by Jewell Parker Rhodes