The answer is very simple. There is no difference. They are more or less synonyms.

However, in modern times we prefer the term tsunami and strongly discourage the term tidal wave. The reason is that there is NOTHING tidal about a Tsunami. Tsunamis are generated when an earthquake, huge landslide or large meteorite impact occurs and displaces a lot of water.

Tides form in response to the sun and moon and have nothing to do with Tsunamis.