late 14c., "part of a curved line," originally in reference to the sun's apparent motion across the sky, from Old French arc "bow, arch, vault" (12c.), from Latin arcus "a bow, arch," from Proto-Italic *arkwo- "bow."

This has Germanic cognates in Gothic arhvazna, Old English earh, Old Norse ör "arrow," from Proto-Germanic *arkw-o- "belonging to a bow." It also has cognates in Greek arkeuthos, Latvian ercis "juniper," Russian rakita, Czech rokyta, Serbo-Croatian rakita "brittle willow." De Vaan sees an Italo-Germanic word for "bow" which can be connected with Balto-Slavic and Greek words for "willow" and "juniper" "under the well-founded assumption that the flexible twigs of juniper or willow were used as bows." The Balto-Slavic and Greek forms point to *arku-; "as with many plant names, this is likely to be a non-IE loanword."

The electrical sense is attested from 1821.

Proto-Indo-European root meaning "to shine," in derivatives "sky, heaven, god."

It forms all or part of: adieu; adios; adjourn; Asmodeus; circadian; deific; deify; deism; deity; deodand; deus ex machina; deva; dial; diary; Diana; Dianthus; diet (n.2) "assembly;" Dioscuri; Dis; dismal; diurnal; diva; Dives; divine; joss; journal; journalist; journey; Jove; jovial; Julia; Julius; July; Jupiter; meridian; Midi; per diem; psychedelic; quotidian; sojourn; Tuesday; Zeus.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit deva "god" (literally "shining one"); diva "by day;" Avestan dava- "spirit, demon;" Greek delos "clear;" Latin dies "day," deus "god;" Welsh diw, Breton deiz "day;" Armenian tiw "day;" Lithuanian dievas "god," diena "day;" Old Church Slavonic dini, Polish dzień, Russian den "day;" Old Norse tivar "gods;" Old English Tig, genitive Tiwes, name of a god.

"belief in the existence of a personal God, generally accompanied by denial of revelation and the authority of a church," 1680s (deist is from 1620s), from French déisme, from Latin deus "god," from PIE root *dyeu- "to shine," in derivatives "sky, heaven, god."

A type of rationalistic theology that rose to prominence in England in the late 17c. and early 18c.; the deists advocated for the sufficiency of natural religion, apart from Scripture or revelation. Until c. 1700, the word was opposed to atheism; later it was the opposite of theism (q.v.), with which it is etymologically equivalent.

The term "deism" not only is used to signify the main body of the deists' teaching, or the tendency they represent, but has come into use as a technical term for one specific metaphysical doctrine as to the relation of God to the universe, assumed to have been characteristic of the deists, and to have distinguished them from atheists, pantheists and theists,—the belief, namely, that the first cause of the universe is a personal God, who is, however, not only distinct from the world but apart from it and its concerns. [Encyclopaedia Britannica, 1922]

Old English clud "mass of rock, hill," related to clod.

The modern sense "rain-cloud, mass of evaporated water visible and suspended in the sky" is a metaphoric extension that begins to appear c. 1300 in southern texts, based on similarity of cumulus clouds and rock masses. The usual Old English word for "cloud" was weolcan (see welkin). In Middle English, skie also originally meant "cloud." The last entry for cloud in the original rock mass sense in Middle English Compendium is from c. 1475.

The four fundamental types of cloud classification (cirrus, cumulus, stratus, nimbus) were proposed by British amateur meteorologist Luke Howard (1772-1864) in 1802.

Meaning "cloud-like mass of smoke or dust" is from late 14c. Figuratively, as something that obscures, darkens, threatens, or casts a shadow, from c. 1300; hence under a cloud (c. 1500). In the clouds "removed from earthly things; obscure, fanciful, unreal" is from 1640s. Cloud-compeller translates (poetically) Greek nephelegereta, a Homeric epithet of Zeus.

*sāwel-, Proto-Indo-European root meaning "the sun." According to Watkins, the *-el- in it originally was a suffix, and there was an alternative form *s(u)wen-, with suffix *-en-, hence the two forms represented by Latin sol, English sun.

It forms all or part of: anthelion; aphelion; girasole; heliacal; helio-; heliotrope; helium; insolate; insolation; parasol; parhelion; perihelion; Sol; solar; solarium; solstice; south; southern; sun; Sunday.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit suryah, Avestan hvar "sun, light, heavens;" Greek hēlios; Latin sol "the sun, sunlight;" Lithuanian saulė, Old Church Slavonic slunice; Gothic sauil, Old English sol "sun;" Old English swegl "sky, heavens, the sun;" Welsh haul, Old Cornish heuul, Breton heol "sun;" Old Irish suil "eye;" Avestan xueng "sun;" Old Irish fur-sunnud "lighting up;" Old English sunne German Sonne, Gothic sunno "the sun."

mid-14c., celynge, "act of paneling a room," noun formed (with -ing) from Middle English verb ceil "put a cover or ceiling over," later "cover (walls) with wainscoting, panels, etc." (early 15c.); from Old French celer "conceal," also "cover with paneling" (12c.), from Latin celare "to hide" (from PIE root *kel- (1) "to cover, conceal, save"). Probably influenced by Latin caelum "heaven, sky" (see celestial).

Extended to the paneling itself from late 14c., then to lath-and-plaster work. The meaning "interior overhead surface of a room" is attested by 1530s; by late 19c. the meaning "wainscoting" was only in provincial English. Figurative sense of "upper limit" is from 1934.

Colloquial figurative phrase hit the ceiling "lose one's temper, get explosively angry" is attested by 1908; earlier it meant "to fail" (by 1900, originally U.S. college slang). Glass ceiling in the figurative sense of "invisible barrier that prevents women from advancing" in management, etc., is attested from 1988.

1570s, in ancient Roman architecture, "entrance-hall," the most important and usually the most splendid apartment of a house. from Latin atrium "central court or first main room of a house, room which contains the hearth," from Proto-Italic *atro-, sometimes said (on authority of Varro, "De Lingua Latina") to be Etruscan.

Watkins suggests it is from PIE root *ater- "fire," on notion of "place where smoke from the hearth escapes" (through a hole in the roof). De Vaan finds this not very compelling, "since soot is black, but not the fire itself," and prefers a different PIE root, *hert-r- "fireplace," with cognates in Old Irish aith, Welsh odyn "furnace, oven," Avestan atarš "fire."

The appurtenance of atrium depends on the interpretation that this room originally contained the fireplace. This etymology was already current in ancient times, but there is no independent evidence for it. Still, there is no good alternative. [de Vaan]

The anatomical sense of "either of the upper cavities of the heart" is recorded by 1870. The meaning "sky-lit central court in a public building" is attested by 1967.

c. 1300 (probably older; piehus "bakery" is attested from late 12c.), "baked dish of pastry filled with a preparation of meats, spices, etc., covered with a thick layer of pastry and baked," from Medieval Latin pie "meat or fish enclosed in pastry" (c. 1300), which is perhaps related to Medieval Latin pia "pie, pastry," also possibly connected with pica "magpie" (see pie (n.2)) on notion of the bird's habit of collecting miscellaneous objects.

According to the OED, the word is not known outside English with the exception of Gaelic pighe, which is from English. In the Middle Ages, a pie had many ingredients, a pastry but one. Fruit pies began to appear c. 1600.

The word in the figurative sense of "something easy" is from 1889; the earlier expression easy as eating pie is by 1884. Slice of the pie in the figurative sense of "something to be shared out" is by 1967. Pie-eyed "drunk" is from 1904. Phrase pie in the sky is attested by 1911, from Joe Hill's Wobbly parody of hymns. Pieman "baker or seller of pies" is by c. 1300 as a surname. Pie chart is from 1922.

1650s, "a crown," from Latin corona "a crown, a garland," in ancient Rome especially "a crown or garland bestowed for distinguished military service" (from a suffixed form of PIE root *sker- (2) "to turn, bend").

With many extended senses in botany, anatomy, etc. As a brand of Cuban cigar, 1876. The brand of Mexican pale lager beer dates from 1925. The astronomical sense of "luminous circle observed around the sun during total eclipses" is from 1809. The two "crown" constellations, Corona Borealis and Corona Australis, both are Ptolemaic.

Corona Borealis "certainly is much more like that for which it is named than usually is the case with our sky figures," according to Richard Hinckley Allen ("Star-Names and Their Meaning," 1899), and he adds that to the Greeks it was stephanos, a wreath, and from Roman times on typically it was Ariadne's Crown. To Arab astronomers, however, it was Al Fakkah "the dish" (sometimes "the pauper's dish" or "the broken dish" — Latinized as Discus parvus confractus — as the celestial circle is incomplete), a word wrestled into European languages as Alphaca or Alphecca, and used as the name of the constellation's none-too-bright brightest star.

first planet discovered that was not known in ancient times, named for the god of Heaven, husband of Gaia, the Earth, from Latin Uranus, from Greek Ouranos literally "heaven, the sky;" in Greek cosmology, the god who personifies the heavens, father of the titans.

The planet was discovered and identified as such in 1781 by Sir William Herschel (it had been observed before, but mistaken for a star; in 1690 John Flamsteed cataloged it as 34 Tauri); Herschel proposed calling it Georgium Sidus, literally "George's Star," in honour of his patron, King George III of England.

I cannot but wish to take this opportunity of expressing my sense of gratitude, by giving the name of Georgium Sidus ... to a star which (with respect to us) first began to shine under His auspicious reign. [Sir William Herschel, 1783]

The planet was known in English in 1780s as the Georgian Planet; French astronomers began calling Herschel, and ultimately German astronomer Johann Bode proposed Uranus as in conformity with other planet names. However, the name didn't come into common usage until c. 1850.