To permeate means to spread through something completely, reaching every part of it. When you bake cookies, the smell of vanilla and butter permeates your entire house, drifting into every room until even your bedroom smells delicious. When rain permeates the soil in a garden, the water soaks all the way through the dirt, reaching deep down to plant roots.

The word suggests a thorough, gradual spreading. Sadness can permeate a room after bad news, affecting everyone's mood. An idea can permeate a culture, becoming part of how everyone thinks. Paint thinner permeates wood, soaking into the grain instead of just sitting on the surface.

Permeate often describes things you can't see moving, but you notice their effects everywhere. You might not watch individual water molecules seeping through coffee grounds, but you know the water has permeated the grounds when your coffee turns dark and flavorful. Similarly, when your teacher's enthusiasm for science permeates the classroom, you don't see it happening, but suddenly everyone is excited about the experiment.

Think of permeate as describing something that doesn't just touch the surface but travels all the way through, like food coloring permeating water in a glass.