sandal
躧 centers on a type of footwear: a sandal. It is a specific character for this item, with no broader abstract extensions.
躧 combines 足 (foot) with 麗, which likely contributes the sound. The character is a phono-semantic compound for a type of shoe.
The left side 足 means foot, and the right side 麗 looks elaborate. Picture a fancy sandal on a foot: 躧 is a sandal.
For シ, imagine a sheer silk sandal: sheer -> シ, and the delicate sandal is on your foot.