水下

under the water / submarine

surname Shui

water / river / liquid / beverage / additional charges or income / (of clothes) classifier for number of washes

down / downwards / below / lower / later / next (week etc) / second (of two parts) / to decline / to go down / to arrive at (a decision, conclusion etc) / measure word to show the frequency of an action

underwater nuclear test

nuclear underwater burst / underwater nuclear explosion