knee-pad
韠 refers specifically to a knee-pad, a protective covering worn over the knee.
韠 combines 韋 (tanned leather) with 畢, which likely contributes a phonetic element. The character denotes a leather knee covering.
The left side 韋 suggests leather, and the right side 畢 looks like a net or covering. Imagine a leather net-like pad strapped over the knee.
For ヒツ, picture a knee-pad that hits the ground when you kneel: hits -> ヒツ, and the leather pad protects your knee.