the point on the surface of the earth or water directly below, directly above, or at which an atomic or hydrogen bomb explodes.
(sometimes initial capital letters) the site of the former World Trade Center in New York City, destroyed in the September 11, 2001 terrorist attacks.
Informal. the very beginning or most elementary level: Some of the students are starting from ground zero.
Origin of ground zero
First recorded in 1945–50
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for ground zero
a point on the surface of land or water at or directly above or below the centre of a nuclear explosion
a scene of great devastation
(sometimes capitals) the name given to the devastated site of the collapsed World Trade Center towers in New York after September 11 2001
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for ground zero
1946, originally with reference to atomic blasts. In reference to the Sept. 11, 2001, terrorist attack on New York, it was in use by Sept. 13.
Online Etymology Dictionary, © 2010 Douglas Harper