bury, inter
瘞 centers on placing something into the ground: burying a body or interring remains. The two given meanings are direct synonyms for this act of burial.
瘞 combines 疒 (sickness) with an inner component that likely contributed the sound and the idea of burial or covering. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around the inner shape like a grave enclosing a body. Picture illness being buried underground, ending its spread.
For エイ, imagine burying a letter 'A' (エイ) in the ground: the 'A' sound cues エイ while the burial scene matches the meaning.