This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 殹 is uncertain. It appears to combine 医 and 殳, but the original meaning and component function are unclear.
The left side looks like a container (医) and the right side is a weapon or tool (殳). Imagine an ancient tool striking a container, but the exact meaning is lost.
For エイ, picture an ancient Egyptian (エイ) hieroglyph of a tool striking a container, matching the shape of 殹.