This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鈝 combines 金 (metal) and 牛 (cow), but the exact historical development and original meaning are uncertain.
No clear meaning is available, so a mnemonic based on shape may help recognition: a metal (金) cow (牛) — perhaps a cow-shaped metal object or bell.
For イン, imagine an inn where a metal cow statue stands in the lobby: inn -> イン, and the metal cow (鈝) is the inn's strange decoration.