This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鏙 combines 金 (metal) with 崔, which likely contributes the sound. The exact historical development is uncertain.
Since the meaning is unclear, focus on the shape: metal 金 beside the tall mountain-like 崔. Picture an unknown metal object found near a mountain.
For サイ, imagine a sigh of frustration when you can't identify this rare metal: sigh -> サイ.