"the galaxy as seen in the night sky," late 14c., loan-translation of Latin via lactea; see galaxy. Formerly in Middle English also Milken-Way and Milky Cercle. The ancients speculated on what it was; some guessed it was a vast assemblage of stars (Democrates, Pythagoras, even Ovid); the question was settled when Galileo, using his telescope, reported that the whole of it was resolvable into stars. Old native names for it include Jacob's Ladder, the Way to St. James's, and Watling Street (late 14c.).
late 14c., from French galaxie or directly from Late Latin galaxias "the Milky Way" as a feature in the night sky (in classical Latin via lactea or circulus lacteus), from Greek galaxias (adj.), in galaxias kyklos, literally "milky circle," from gala (genitive galaktos) "milk" (from PIE root *g(a)lag- "milk").
The technical astronomical sense in reference to the discrete stellar aggregate including the sun and all visible stars emerged by 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"]
Originally ours was the only one known. 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 in the affirmative until the 1920s.
originally the name of the river, from Dakota (Siouan) mnisota, literally "cloudy water, milky water," from mni "river, stream" + sota "slightly clouded." As the name of a U.S. territory from 1849 (admitted as a state 1858). Related: Minnesotan (by 1867).