Seism

This is an earthquake, basically.

We rarely see it in this form, however. It’s the root of the word “seismic,” which is how we would normally read it. In fact, none of the resources I consulted had any examples for seism, though they each had a lot for seismic and seismal.

The origin is the Greek “seismos” which means “shaking Earth.” Seism has become a prefix, essentially, though it remains a standalone word.

Why I Looked It Up

A NY Times Crossword clue was:

Might precede an extinction event