This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鏄 combines 金 (metal) with 專, which likely contributes the sound. The exact historical development is uncertain.
The left side 金 suggests metal, and the right side 專 looks like a specialized tool. Imagine a lump of iron (てつのかたまり) being worked into something useful.
For タン, picture a tan-colored lump of metal: tan -> タン, and the 金 component reinforces the metal idea.