This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 臋 is uncertain. It visually combines 殿 on top and 肉 (flesh/meat) on the bottom, but the original semantic and phonetic roles are unclear.
The top part 殿 suggests a palace or hall, and the bottom 肉 is flesh. Without a clear meaning, you might imagine a rare cut of meat served in a grand hall, but this is purely a mnemonic device.
For デン, picture a den in a palace where rare meat is stored: den -> デン, tying the top 殿 (palace) and bottom 肉 (meat) together.