Tidal describes anything related to tides, the regular rise and fall of ocean water levels caused by the gravitational pull of the moon and sun. When you visit the beach, you might notice the tidal zone, where water covers the sand at high tide but leaves it exposed at low tide. This area gets washed over twice each day as the ocean rises and retreats.

The power of tides can be enormous. Tidal wave is a name people sometimes use for a giant wave caused by underwater earthquakes or volcanic eruptions that can devastate coastal areas. Today, scientists prefer to call these waves tsunamis instead of tidal waves, because they are not actually caused by tides. Tidal currents are strong flows of water created as tides move in and out of bays and harbors, powerful enough to carry boats or swimmers. Some places harness this energy: tidal power plants generate electricity from the predictable movement of tides.

The word also describes anything that comes in waves or surges, like a crowd. If your school principal announces free ice cream at lunch, you might see a tidal wave of students rushing toward the cafeteria. When used this way, tidal suggests something powerful, overwhelming, and hard to stop, just like the ocean itself.