tidal wave

noun

• A large and sudden rise and fall in the tide.
• A 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."

• A large, sudden inundation of water from the storm surge, or waves of that surge.
• A sudden and powerful surge.

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

• A crest of ocean water; a wave.
• A crest of ocean water resulting from tidal forces.