galaxy (n.) Look up galaxy at Dictionary.com
late 14c., from Old French galaxie, from Late Latin galaxias "Milky Way," from Greek galaxias (adj.), in galaxias kyklos, literally "milky circle," from gala (genitive galaktos) "milk" (see lactation). The technical astronomical sense emerged 1848. Figurative sense of "brilliant assembly of persons" is from 1580s. Milky Way is a translation of Latin via lactea.
See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. [Chaucer, "House of Fame"]
Astronomers began to speculate by mid-19c. that some of the spiral nebulae they could see in telescopes were actually immense and immensely distant structures the size and shape of the Milky Way. But the matter was not settled until the 1920s.