Okay, so you know how dinosaurs lived a long, long time ago? Well, some of the words we use today are also very old, just like the dinosaurs. We call them "fossil words".
These words were commonly used a really long time ago, but they aren't used as much anymore. Just like how we don't see dinosaurs around anymore, we don't see these words around as much either.
But, sometimes we still hear or read these words, especially in older books or movies. People might use them to sound fancy or because they think they sound cool.
Some examples of fossil words are "thou" instead of "you", "hither" instead of "here", and "whence" instead of "where". They might sound a bit strange or old-fashioned to us now, but they were once widely used.
So, just like how we can learn about dinosaurs by looking at their fossils, we can learn about the language of the past by looking at these fossil words!