name of fief in Shandong bestowed on the eldest son of Wen Wang
郜 is a rare kanji that refers to a specific historical place name: a fief in Shandong granted to the eldest son of King Wen. Its meaning is limited to this proper-noun usage.
郜 combines 告 (likely phonetic) with the city/walled-town component ⻏, forming a place name. The exact historical development is uncertain beyond its use as a proper noun.
The left side 告 (announce) and the right side ⻏ (city) together suggest a place that was officially announced or granted: the fief of 郜.
For コウ, imagine the eldest son announcing (告) his new fief to the city (⻏) with a proud call: 'Kou!' The sound 'Kou' cues コウ.
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