The word 'Tsunami' is of Japanese origin, derived from two kanji characters: 'tsu' (津) meaning 'harbour' and 'nami' (波) meaning 'wave'. It refers to a series of extremely long-wavelength ocean waves generated by sudden tectonic displacement of water (subsea earthquakes, landslides, or volcanic eruptions).

Option analysis:

• Tsunami: Correct, literally translates to 'harbour wave' from Japanese.
• Hurricane: Derived from Taino word 'Huracan', meaning evil spirit of wind.
• Cyclone: Coined from Greek 'kyklos', meaning coiled snake or wheel.
• Seiche: French-Swiss term for standing waves in enclosed water bodies.

In clear, oligotrophic open ocean water, water molecules selectively absorb longer wavelengths (red, orange, and infrared) within the top $10$ to $20\text{ meters}$. Shorter wavelengths with higher energy, specifically blue light (wavelengths between $400$ and $480\text{ nm}$), experience the lowest absorption coefficient and penetrate deepest into the photic zone, reaching depths up to $200\text{ meters}$.

Option analysis:

• Red: Longest visible wavelength ($\gt 650\text{ nm}$), absorbed first in the top $10\text{ m}$.
• Blue: Correct, penetrates deepest in clear open ocean waters.
• Green: Penetrates deeply in coastal turbid waters, but blue penetrates deeper in open ocean.
• Yellow: Intermediate penetration ($50\text{ m}$).

In ocean wave mechanics, the crest is the highest point or elevation of a wave cycle above the still water line. The trough is the lowest point or depression. The vertical distance between crest and trough is wave height ($H$), and the horizontal distance between two consecutive crests is wavelength ($\lambda$).

Option analysis:

• Crest: Correct, highest peak of a wave.
• Trough: Lowest point or valley of a wave.
• Current: Net horizontal transport of water masses.
• Heave: Linear vertical bodily motion of a vessel or water particle.