This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鎈 combines 金 (metal) with 差, which likely contributes the sound. The exact historical development is uncertain.
The left side is metal 金, and the right side is 差 (difference). Without a clear meaning, picture a mysterious metal object that looks slightly different from others.
For サ, imagine a saw made of metal: saw -> サ, and the metal 金 on the left hints at the tool.