cutting off feet as form of punishment
刖 centers on a specific ancient punishment: cutting off the feet. The meaning is narrow and concrete, with no common abstract extensions.
刖 combines 月 (flesh/body part) with 刂 (knife), suggesting cutting a body part. The specific punishment meaning is historically attested, but the exact development is uncertain.
The left side 月 represents flesh or a body part, and the right side 刂 is a knife. Picture a knife cutting off flesh at the feet as a harsh punishment.
For ゲツ, imagine a guard saying 'Get you!' as they prepare to carry out the punishment: 'Get you' -> ゲツ, and the knife cuts off the feet.