This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
壡 appears to be a rare variant or compound of 叡 with 土 added inside. The exact historical development is uncertain.
The outer shape 叡 is associated with intelligence or clarity, and the inner 土 is earth. Without a clear meaning, picture a bright insight buried in the ground, waiting to be uncovered.
For エイ, imagine an ancient sage named Ei who carved the character 壡 into the earth: Ei -> エイ, and his wisdom is hidden in the soil.