This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
斦 visually doubles the 斤 (axe) component, but its historical origin and meaning are uncertain. It may be an archaic variant or a character whose usage has been lost.
Two axes 斤 side by side suggest doubling or balance, but the actual meaning is unclear. Think of it as a mysterious double-axe symbol.
For ギン, imagine two silver (銀, ぎん) axes crossed: 銀 -> ギン, and the double axe shape reinforces the reading.