water chestnut
荸 refers specifically to the water chestnut plant. The meaning is narrow and concrete, without broader abstract extensions.
荸 combines the plant radical 艹 with 孛, which likely provides the sound. The exact historical development of this character is uncertain.
The plant top 艹 sits above 孛, like a water chestnut plant growing out of the water. The lower part suggests the round, knobby shape of the chestnut itself.
For ホツ, imagine a water chestnut popping out of the water with a sharp 'hots!' sound: hots -> ホツ, as the plant bursts into view.
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