fat, gross, sleek
臕 centers on excess flesh or fat, giving the idea of something grossly plump or sleekly well-fed. The meanings 'fat', 'gross', and 'sleek' all describe a body condition of being thick or filled out.
臕 combines the flesh radical ⺼ with 麃, which likely contributes the sound and relates to a plump or fat animal. The exact historical development is uncertain.
The flesh radical ⺼ on the left suggests a body part, while the right side 麃 looks like a well-fed deer-like creature. Together they picture a plump, sleek animal with plenty of fat.
For ヒョウ, imagine a fat, sleek leopard (ヒョウ) lounging after a big meal: ヒョウ -> ヒョウ, and its plump belly shows the meaning of fat and sleek.