sole of foot
蹠 refers specifically to the sole of the foot, the underside that touches the ground.
蹠 combines 足 (foot) with 庶, which likely contributes the sound. The exact historical development is uncertain.
The left side 足 means foot, and the right side 庶 looks like a shelter. Imagine the sole of your foot as the part that shelters you from the ground when you walk.
For セキ, picture stepping on a wet deck: the sole of your foot gets seki (セキ) from the damp wood.
antipodal; diametrical opposition
antipodes
antipodes; antipode
diametrically opposed; antipodal
palmoplantar pustulosis
sole (of the foot)
footpad dermatitis (in animals); FPD
plantigrade (walking on the soles of the feet)
metatarsal