abundant, numerous, crowd
甡 centers on abundance through duplication: two 生 (life/growth) side by side suggest a crowd, numerous things, or plentiful life.
甡 is formed by doubling 生 (life, growth), likely to emphasize abundance or a crowd of living things. The exact historical development is uncertain, but the reduplication pattern is a common way to intensify meaning.
Two 生 (life) characters standing together like a crowd: life multiplied means abundant and numerous.
For シン, imagine a scene of abundant life: a shin-deep field of growing sprouts (シン sounds like 'shin'), where every step reveals more life.
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