state in today's Hubei province
鋐 is a rare kanji whose given meaning is a historical place name: a state in today's Hubei province. It has no clear standalone conceptual center beyond that specific reference.
鋐 is a phono-semantic compound: 金 (metal) suggests a metal object or tool, while 宏 likely provides the sound. The exact historical development is uncertain, and the character is rare.
The left side 金 (metal) and right side 宏 (wide, vast) together can suggest a vast metal object or a metal vessel, but the actual meaning is a specific place name. Picture a large bronze vessel inscribed with the name of an ancient state in Hubei.
For コウ, imagine a wide (宏) metal (金) gong: gong -> コウ, and the sound echoes across the ancient state.