Definition of ground zero
1
: the point directly above, below, or at which a nuclear explosion occurs
2
: the center or origin of rapid, intense, or violent activity or change
broadly
: center sense 2a
the party town that served as ground zero for those corporate … bashes — Rich Eisen
3
: the very beginning : square one
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Merriam-Webster unabridged
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Time Traveler for ground zero
The first known use of ground zero was in 1946
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