river in Shandong province
濼 is a rare kanji that refers specifically to a river in Shandong province. Its meaning is a proper geographic name with no broader conceptual center.
濼 combines the water radical 氵 with the phonetic component 樂, suggesting a name for a body of water. The exact historical development is uncertain.
The water radical 氵 beside 樂 points to a specific river. Imagine a musical festival (樂 can suggest music) by the Luo River in Shandong.
For ロク, picture a lock on a map marking the exact spot of this river: lock -> ロク, and the water radical 氵 reinforces the river location.
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