as a conventional title of courtesy before a man's Christian name, mid-15c., unaccented variant of master (n.), but without its meaning. As a form of address when the man's name is unknown (often with a tinge of rudeness), from 1760.
The disappearance of master and mister, and the restricted and obsolescent use of sir, as an unaccompanied term of address, and the like facts with regard to mistress, Mrs., and madam, tend to deprive the English language of polite terms of address to strangers. Sir and madam or ma'am as direct terms of address are old-fashioned and obsolescent in ordinary speech, and mister and lady in this use are confined almost entirely to the lower classes. [Century Dictionary, 1895]
late 14c., "Roman god of the sea," from Latin Neptunus, the Roman god of the sea (son of Saturn, brother of Jupiter, later identified with Greek Poseidon), probably from PIE root *nebh- "cloud" (source of Latin nebula "fog, mist, cloud"), via a sense of "moist, wet."
The planet so named was discovered by German astronomer Johann Gottfried Galle (1812-1910) on the night of Sept. 23-24, 1846 and named by French astronomer Urbain Le Verrier (1811-1877), who had predicted its position based on anomalies in the motion of Uranus and sent the coordinates to Galle. It is too dim to be seen with the naked eye, but it had been seen by observers using telescopes as far back as Galileo, but they did not recognize and identify it as a planet. Until the identification of Pluto in 1930 (and since that planet's demotion), it was the most distant known planet of the solar system.
loose ("open") star cluster (M44) in Cancer, 1650s, from Latin praesaepe the Roman name for the grouping, literally "enclosure, stall, manger, hive," from prae "before" (see pre-) + saepire "to fence" (see septum).
It is similar to the Hyades but more distant, about 600 light-years away (as opposed to about 150 for the Hyades), consists of about 1,000 stars, mostly older, the brightest of them around magnitude 6.5 and thus not discernible to the naked eye even on the clearest nights, but their collective light makes a visible fuzz of nebular glow that the ancients likened to a cloud (the original nebula); Galileo was the first to resolve it into stars (1609).
The modern name for it in U.S. and Britain, Beehive, seems no older than 1840. Greek names included Nephelion "Little Cloud" and Akhlys "Little Mist." "In astrology, like all clusters, it threatened mischief and blindness" [Richard Hinckley Allen, "Star Names and Their Meanings," 1899].
"Manger" to the Romans perhaps by influence of two nearby stars, Gamma and Delta Cancri, dim and unspectacular but both for some reason figuring largely in ancient astrology and weather forecasting, and known as "the Asses" (Latin Aselli), supposedly those of Silenus.