This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form combines 竹 (bamboo) with 榴, but the original semantic and phonetic roles are unclear.
The top 竹 suggests bamboo, and the bottom 榴 contains 木 (tree) and 田 (field), but the overall meaning is unclear. Picture an obscure bamboo tool or container whose use has been forgotten.
For リュウ, imagine a rare bamboo artifact labeled with the invented name 'Ryuu' (リュウ), like a mysterious relic whose purpose is lost.
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