This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鉹 combines 金 (metal) with 多, but the exact historical development is uncertain. It may have been a phono-semantic compound, but the original meaning is unclear.
The kanji visually contains 金 (metal) and 多 (many), but since its meaning is uncertain, no reliable mnemonic can be built from the components.
For シ, imagine a sheet of metal with many holes: sheet -> シ, tying the metal component to the reading.