This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
銒 combines 金 (metal) with 幵, but the exact historical development is uncertain. It may have originally referred to a metal vessel or container.
The left side is metal 金, and the right side 幵 looks like a lid or cover. Picture a metal container with a lid, perhaps for holding sake or stew, but its exact meaning is unclear.
For ケイ, imagine a metal container shaped like the letter K: K -> ケイ, and the container is made of 金.