This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
湉 combines the water radical 氵 with 恬, which likely contributes the sound. The exact historical development is uncertain.
Water 氵 beside a calm heart 恬 suggests still, peaceful water, but the actual meaning is uncertain.
For テン, imagine ten テン tranquil ponds: ten -> テン, and the water 氵 stays calm like the heart 恬.
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