calm, quiet, bland, rocking, rippling, suffice
澹 centers on a state of gentle, undisturbed motion or stillness: calm water that ripples softly, a quiet and bland demeanor, or a sense of sufficiency that settles without excess.
澹 combines 氵 (water) with 詹, which likely contributes the sound. The character originally referred to water that is calm or gently rippling, and later extended to blandness or quietness.
Water 氵 beside 詹: imagine a quiet pond where the surface barely moves, just a soft ripple now and then. That calm, bland stillness is 澹.
For タン, picture a tan-colored pond so calm it looks like a flat, bland surface: tan -> タン, and the water is perfectly still.
dark; gloomy; somber; depressing