This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
寱 is a rare character whose exact historical development is uncertain. It visually contains 宀 (roof) and 爿 (bed) with a complex inner component 臬, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture a mysterious room under a roof 宀 where a bed 爿 sits beside an unknown object 臬—its purpose is uncertain.
For ゲイ, imagine a gate ゲイ (like ゲート) leading into this mysterious room: gate -> ゲイ, and you enter the unknown space.