This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 臡 is uncertain. It visually combines 難 (difficult) and 肉 (meat), but the original semantic and phonetic roles are unclear.
With no clear meaning, picture a difficult piece of meat: 難 on top of 肉, something hard to chew or digest.
For デイ, imagine a day when you struggle with a tough piece of meat: day -> デイ, and the difficult meat 臡 ruins your meal.