giant tsunami; large tsunami
Refers to a tsunami of exceptionally large scale, often defined by the JMA as over 3 meters in height. The term 'giant tidal wave' is an older English equivalent but less precise.
A giant tsunami struck the coast during the Great East Japan Earthquake.
The Japan Meteorological Agency issued a major tsunami warning.
major tsunami warning
Compound of 大 (おお, 'big') and 津波 (つなみ, 'tsunami'). The reading おおつなみ follows standard rendaku rules.