This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鈜 combines 金 (metal) with 厷, which likely contributes the sound. The exact historical development is uncertain.
The left side is metal 金, and the right side 厷 looks like a bent arm. Picture a metal arm brace, but remember the meaning is uncertain.
For コウ, imagine a metal gong: the sound 'gong' is close to コウ, and the metal radical 金 fits the scene.