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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

The first is some sort of “event” — like the COVID-19 pandemic or 9/11.

From MarketWatch • Jun. 25, 2026

Stranded abroad by the 9/11 attacks, he hitched a ride back on an air force tanker and was at his desk the next day.

From The Wall Street Journal • Jun. 22, 2026

Critics said Greenspan's policy of low interest rates after 9/11 had fuelled a sharp rise in house prices and over-enthusiastic selling of mortgages by banks.

From BBC • Jun. 22, 2026

Peter Thiel, the arch-conservative PayPal co-founder, believed better data-sharing between agencies might have prevented 9/11, and built the company around a mission of "defending the West."

From Barron's • Jun. 18, 2026

In the months after 9/11, a whole series of questions arose as to whether to retaliate, how to retaliate, and who to retaliate against.

From "Words Like Loaded Pistols" by Sam Leith