Etymology

Dear Gotham City,

What is the etymology of "Ground Zero"? I often hear 'ground zero' mentioned with regard to WTC suicide attacks.

Where does the phrase (especially 'zero') come from?

Well, kids, Merriam-Webster dates it from 1946. I believe it was used to help describe the effects of the atom bombs dropped on Hiroshima and Nagasaki.

Ground zero is the point on the ground closest to where the blast occurred, so specifying a distance from this point describes what the radius is from the closest point to the explosion.

It's since been expanded as a metaphor for all kinds of things, many of them non-destructive.

"Milan is ground-zero for raised hemlines", for example.