Middle English word ei comes from Proto-Indo-European *h₂éwis (Bird.)

Detailed word origin of ei

Dictionary entry	Language	Definition
*h₂éwis	Proto-Indo-European (ine-pro)	Bird.
*ōjóm	Proto-Indo-European (ine-pro)
*ojóm	Proto-Indo-European (ine-pro)
*ajjan	Proto-Germanic (gem-pro)
*ajją	Proto-Germanic (gem-pro)	Egg.
ǣġ	Old English (ang)
ei	Middle English (enm)	An egg, especially of a chicken or other fowl.

Words with the same origin as ei