grebe, (kokuji)
鳰 is a Japanese kokuji that refers specifically to the grebe, a type of water bird. It has no extended abstract meanings.
鳰 is a kokuji created in Japan by combining 入 (enter) and 鳥 (bird). The exact reasoning is uncertain, but it may relate to the grebe's diving behavior.
A bird 鳥 that enters 入 the water: that's a grebe, a diving water bird.
For にお, imagine a grebe diving into a pond and making a soft 'ni-o' ripple sound as it enters: にお.
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