1769, short for stella polaris, Modern Latin, literally "the pole star" (see polar). The ancient Greeks called it Phoenice, "the Phoenician (star)," because the Phoenicians used it for navigation. Due to precession of the equinoxes the pole was a few degrees off (closer to Beta Ursae Minoris), but evidently Polaris was close enough. Also see pole (n.2). The Old English word for it was Scip-steorra "ship-star," also reflecting its importance in navigation. As the name of a U.S. Navy long-range submarine-launched guided nuclear missile, it dates from 1957.
late 14c., Pliades, "visible open star cluster in the constellation Taurus," in Greek mythology they represent the seven daughters of Atlas and Pleione, transformed by Zeus into seven stars. From Latin Pleiades, from Greek Pleiades (singular Plēias), perhaps literally "constellation of the doves" from a shortened form of peleiades, plural of peleias "dove" (from PIE root *pel- "dark-colored, gray"). Or perhaps from plein "to sail," because the season of navigation begins with their heliacal rising.
Old English had the name from Latin as Pliade. The star cluster is mentioned by Hesiod (pre-700 B.C.E.); only six now are visible to most people; on a clear night a good eye can see nine (in 1579, well before the invention of the telescope, the German astronomer Michael Moestlin (1550-1631) correctly drew 11 Pleiades stars); telescopes reveal at least 500. Hence French pleiade, used for a meeting or grouping of seven persons.