If you've ever felt so terrified you couldn't move, you've been petrified. Someone who's petrified of public speaking will do anything they possibly can to avoid giving a speech.
Petrified is from the French pétrifier, "change into stone," and the Latin root petra, "rock or crag." Its earliest definition was "converted into a stony substance," and this literal meaning describes certain rocky fossils that developed from softer organic matter, like wood. The figurative use, for a person who's so scared it seems like they're made of stone, is attributed from the 18th century.