jaundice
疸 centers on the medical condition jaundice, a yellowing of the skin and eyes caused by liver or bile issues.
疸 combines 疒 (sickness) with 旦, which likely provides the sound タン. The character is used specifically for jaundice.
The sickness enclosure 疒 surrounds 旦, like a yellow dawn light trapped inside the body, causing jaundice.
For タン, imagine a patient with jaundice getting a tan under a sunlamp: tan -> タン, but the yellow skin is from sickness, not the sun.
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