1807, a hybrid formation from tide (q.v.) + Latin-derived suffix -al. A tidal wave (1830) is properly high water caused by movements of the tides; erroneous use for "tsunami, great ocean wave caused by an earthquake, etc." is recorded from 1878.
Main Entry: tid·al Pronunciation: 'tId-&l Function: adjective : of, relating to, or constituting tidal air tidal exchange of the lungs —F. R. Mautz & R. M. Hosler>