ground zero · noun1
From ground + zero, first attested in a June 1946 a report by the United States Strategic Bombing Survey on the atomic bombing of Hiroshima and Nagasaki, Japan, on August 6 and 9, 1945, during World War II. “Zero” was used as the code name for the location of the Trinity atomic bomb test – the first detonation of a nuclear weapon – in New Mexico, USA, on July 16, 1945.
Ground Zero · proper noun2
From the general term ground zero.
Etymology from Wiktionary, CC BY-SA 4.0.