tidal wave

plural tidal waves

1. A large and sudden rise and fall in the tide.
2. proscribedA large, sudden, and disastrous wave of water caused by a tremendous disturbance in the ocean; a tsunami. (See Usage notes below.)

   The last tidal wave here killed twenty and left thousands homeless.

3. proscribedA large, sudden inundation of water from the storm surge, or waves of that surge; a sudden surge of river water.

   1 more example

   During the day conditions worsened quickly—for example, a 2-6-0 on the Uckfield line suddenly encountered flood water high enough to enter its ashpan and extinguish its fire—until lock gates up-river at Barcombe gave way and a tidal wave rolled down the valley meeting head-on a spring tide rolling up from the coast.

   1961 January, “Talking of Trains: Flooding at Lewes”, in Trains Illustrated, page 5

4. figurativelyA sudden and powerful surge.

   I was overcome by a tidal wave of emotions.

   2 more examples

   As the doors opened, a tidal wave of people flooded into the room.

   But this is no stream, folks. This will be a tidal wave that can swamp our democracy.

   2003, Michael Moore, chapter 3, in Dude, Where’s My Country

5. archaicA crest of ocean water; a wave.
6. geographyA crest of ocean water resulting from tidal forces.