Proto-Indo-European root meaning "to flow."

It forms all or part of: fletcher; fledge; flee; fleet (adj.) "swift;" fleet (n.) "group of ships under one command;" fleet (v.) "to float, drift; flow, run;" fleeting; flight (n.1) "act of flying;" flight (n.2) "act of fleeing;" flit; float; flood; flotsam; flotilla; flow; flue; flugelhorn; fluster; flutter; fly (v.1) "move through the air with wings;" fly (n.) "winged insect;" fowl; plover; Pluto; plutocracy; pluvial; pneumo-; pneumonia; pneumonic; pulmonary.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit plavate "navigates, swims;" Greek plynein "to wash," plein "to navigate," ploein "to float, swim," plotos "floating, navigable," pyelos "trough, basin;" Latin plovere "to rain," pluvius "rainy;" Armenian luanam "I wash;" Old English flowan "to flow;" Old Church Slavonic plovo "to flow, navigate;" Lithuanian pilu, pilti "to pour out," plauju, plauti "to swim, rinse."

god of the dead in Greek mythology; also the name of his realm, the abode of the dead spirits, 1590s, from Greek Haidēs, in Homer the name of the god of the underworld, son of Kronos and Rhea, brother of Zeus and Poseidon. His name is of unknown origin. Perhaps literally "the invisible" [Watkins], from privative prefix a- + idein "to see" (from PIE root *weid- "to see"). The name of the god was extended in later Greek writing to his kingdom, also "the grave, death." Related: Hadal (adj.), 1964; Hadean.

The dead seem all alive in the humane Hades of Homer, yet cannot well speak, prophesie, or know the living, except they drink blood, wherein is the life of man. And therefore the souls of Penelope's Paramours conducted by Mercury chiriped like bats, and those which followed Hercules made a noise but like a flock of birds. [Browne, "Urn-Burial," 1658]

Roman underworld god, from Latin Dis, contracted from dives "rich," which is related to divus "divine, god" (from PIE root *dyeu- "to shine," in derivatives "sky, heaven, god"), hence "favored by god." Compare Pluto and Old Church Slavonic bogatu "rich," from bogu "god."

"plutocracy," 1640s, from Greek ploutos "wealth" (see Pluto) + -archy "rule" on model of monarchy, etc.

"government by the wealthy class; a class ruling by virtue of wealth," 1650s, from Greek ploutokratia "rule or power of the wealthy or of wealth," from ploutos "wealth" (see Pluto) + -kratia "rule" (see -cracy). Synonym plutarchy is slightly older (1640s). Pluto-democracy "plutocracy masquerading as democracy" is from 1895.

"spokesman for plutocrats, one who justifies the interests of the wealthy," 1894, from Greek ploutos "wealth" (see Pluto) + ending from demagogue.

"worship of wealth," 1875, from Greek ploutos "wealth" (see Pluto) + -latry "worship of." Related: Plutolater.

1650s, "mad pursuit of wealth," from Greek ploutos "wealth" (see Pluto) + mania. As a form of insanity, "imaginary possession of wealth," from 1894. Related: Plutomaniac.

1660s, "pertaining to the god Pluto," from Latin Plutonius, from Greek Ploutōnius, from Ploutōn "pertaining to Pluto" (see Pluto). Geological sense is from 1828 (see plutonic). Planetary sense by 1952.

"pertaining to or involving intense heat deep in the earth's crust," 1796, coined by Irish scientist Richard Kirwin (1733-1812) from combining form of Pluto (as god of the underworld) + -ic. Especially in reference to early 19c. geological theory (championed by Hutton) that attributed most of the present features of the earth's crust to action of internal heat, a theory which triumphed over its rival, neptunism, which attributed them to water. Related: Plutonism; Plutonist.

Plutonic rocks are such igneous rocks as have been formed under conditions of depth and pressure, and have cooled slowly, so as to have acquired in general a distinctly crystalline structure ; the term Plutonic is opposed to volcanic, the former designating rocks formed at some depth beneath the surface, the latter rocks of igneous origin but of superficial formation. As used by Lyell, the word is nearly the equivalent of metamorphic. [Century Dictionary, 1895]