The word 'tsunami' entered English in the late 19th century as a direct loanword from Japanese (津波). It is a compound of the Japanese elements 'tsu' (津), meaning 'harbour', and 'nami' (波), meaning 'wave'. The term literally translates to 'harbour wave', reflecting the observation that these destructive waves are most noticeable and damaging when they reach coastal harbours and inlets. While the phenomenon is global, the Japanese term was adopted internationally due to Japan's frequent experience with such events and its scientific study of them, eventually replacing the older English term 'tidal wave', which is a misnomer as tsunamis are unrelated to tides.

This word is a direct borrowing from Japanese, where it is a compound noun. It is not segmented into meaningful morphemes within the English spelling system.