This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
黋 combines 光 (light) outside with 黃 (yellow) inside. The exact historical development is uncertain, but it likely relates to a bright or yellowish light.
The kanji visually contains 光 (light) surrounding 黃 (yellow). Imagine a glowing yellow light, but remember its actual meaning is unclear.
For コウ, picture a bright yellow light glowing like a 光 (こう) beam: 光 -> コウ, and the light shines from inside 黋.
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