lameness, paralysis of hands, leg
瘸 centers on physical impairment of limbs: lameness in the legs or paralysis affecting the hands. The meanings are linked by the idea of a body part losing normal function.
瘸 combines 疒 (sickness) with a phonetic component that is visually 痂 enclosing 肉. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to physical ailment.
The sickness enclosure 疒 wraps around 痂 and 肉, like a disease affecting the flesh. Picture a leg or hand trapped inside, unable to move properly.
For カ, imagine a lame person using a cane: cane -> カ, and the cane helps them walk despite the lameness.
—