Tidal wave

Etymology

From "tidal," relating to the tides (Old English "tīd," time), plus "wave." Strictly, a tidal wave is the crest of water raised by the gravitational pull of moon and sun. The word became the everyday label for catastrophic waves, though scientists prefer "tsunami" precisely because those waves have nothing to do with tides.

noun phrase · /TY-duhl wayv/
A large, powerful ocean wave — popularly used for a destructive one, though the term is a misnomer for a tsunami.
What it names
A common confusion between waves driven by tides and waves driven by sudden displacement — one its misuse usefully exposes.
Example
Newspapers called it a tidal wave, but the geologists were careful to correct them: it was a tsunami triggered by the quake.
Related idea
Often used interchangeably with tsunami, but the distinction matters: a tsunami is caused by the sudden displacement of water — an earthquake, landslide, or eruption — not by the tides at all, which is why the older term is now discouraged in scientific use.