An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) An oval or round object laid by a female bird, reptile, fish, or invertebrate, usually containing a developing embryo. The eggs of birds are enclosed in a chalky shell, while those of reptiles are in a leathery membrane.
2) Biology: The female reproductive cell in animals and plants; an ovum (OxfordDictionaries.com).

M.E., from Old Norse egg, cognate with O.Saxon, M.Du., Du., O.H.G., Ger. Ei, probably from PIE *owyo-/*oyyo- "egg;" source of Pers. xâg, as below.

Toxm, → seed.
Xâg "egg," Lori, Laki xâ, Pash. hâ "egg," Ossetic ajk "egg," Bojnurdi hek "egg," Khotanese āhaa- "egg;" variant xâyé "egg; testicle;" Mid.Pers. xâyak "egg;" Av. aēm/aiam "egg;" cf. Gk. oion, L. ovum; Goth. ada; O.E. æg; Ger. Ei; PIE *owyo-/*oyyo- "egg."