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9/11or 9-11 (nīn′ĭ-lĕv′ən)
September 11, 2001, the date on which two hijacked airliners were flown into the World Trade Center in New York City and another into the Pentagon. A fourth hijacked airliner crashed in open land in Pennsylvania.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.