river in Shandong province
汶 is a proper noun referring to a specific river in Shandong province. It has no general conceptual meaning beyond this geographical name.
汶 combines the water radical 氵 with 文, which likely provides the sound. It is primarily used as a place name for a river in Shandong. The exact historical development is uncertain.
The water radical 氵 beside 文 suggests a river whose name sounds like 文. Picture a river in Shandong with a sign written in elegant script (文) floating on the water.
For ブン, imagine a bun (ブン) floating down the river: the bun cues ブン while the water radical keeps the river scene.
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