This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鐍 combines 金 (metal) with 矞, which likely contributes the sound. The exact historical development is uncertain.
With 金 (metal) on the left and the complex 矞 on the right, 鐍 looks like a metal object, but its specific meaning is unclear.
For ケツ, imagine a metal tool that makes a sharp 'kets' sound when struck: kets -> ケツ.