A body of water with no current or movement; calm, undisturbed water that is completely still.
A compound word from 'still' (without movement) + 'water' (the liquid). The term is descriptive rather than derived, used in English since at least the 1600s.
Still water actually isn't always peaceful—the phrase 'still waters run deep' warns that quiet things can hide danger, and in physics, still water is perfect for studying how light behaves!
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