to castrate
剦 centers on the act of castration, specifically the surgical removal of reproductive organs.
剦 combines 奄 (cover, conceal) with 刂 (knife), suggesting a cutting action that is covered or hidden, fitting the meaning of castration. The exact historical development is uncertain.
A knife (刂) is used to cut what is concealed (奄), representing the act of castration.
For エン, imagine the procedure ending with a clean cut: end -> エン, as the knife finishes the castration.