An Etymological Dictionary of Astronomy and Astrophysics

The diffuse glowing band of light seen on dark nights spanning the sky as a great circle. It is produced by light from stars and nebulae in the → Galactic plane. The apparent form of the Milky Way in the sky results from a geometrical effect created by our location in the outlying regions of a huge, flattened disk of stars. → Milky Way galaxy.

Etymology (EN): From L.L. galaxias “Milky Way,” from Gk. galaxis kyklos “emilky circle,” from gala (gen. galaktos) “milk.”

In Gk. mythology, Jupiter, hoping to immortalize his infant son Hercules (who was born to a mortal woman), placed the baby on Juno’s breast. Her milk spilled up, forming the Milky Way.
Milky, from milk; M.E.; O.E. meol(o)c, (Anglian) milc; cf. Gr. Milch, Goth. miluks; akin to L. mulgere, Gk amelgein “to milk;” PIE base *melg- “wiping, stroking;” → way.

Etymology (PE): Râh, → way; širi, adj. of šir “milk;” Mid.Pers. šir; cf. Skt. ksira- “milk.”