fortress embankment, village
塢 centers on a raised earthen structure used for defense or settlement: a fortress embankment or a fortified village.
塢 combines 土 (earth) with 烏, which likely contributes the sound. The character refers to an earthen embankment or fortified village.
The left side is earth 土, and the right side is a crow 烏. Picture a crow perched on a high earthen wall surrounding a village: the earth and crow together mark a fortress embankment.
For オ, imagine an old crow sitting on the earthen wall: old -> オ, and the old crow guards the fortress.
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