To petrify means to make someone so frightened that they can't move or think clearly. When you're petrified, fear freezes you in place like you've turned to stone. A student might feel petrified before giving a speech in front of the whole school, standing on stage with their mind blank and their feet glued to the floor. A loud crash in the middle of the night might petrify you for a few seconds before you realize it was just the cat knocking over a lamp.

The same idea of turning to stone gives us the scientific meaning of petrify: the process where organic material actually does turn to stone over millions of years. When wood petrifies, minerals slowly replace the wood's cells until it becomes solid rock that still looks like wood. Petrified wood found in places like Arizona's Petrified Forest shows trees that lived 200 million years ago, now preserved as colorful stone.

When someone says they're petrified of something like heights or spiders, they mean terrified, though they probably won't literally freeze. The word petrifying describes anything scary enough to stop you in your tracks.