noun Date: 1946 the point directly above, below, or at which a nuclear explosion occurs, the center or origin of rapid, intense, or violent activity or change, the very beginning ; square one
GROUND ZERO
Meaning of GROUND ZERO in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012