Etymology
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terrestrial (adj.)
late 14c., "of or pertaining to the earth," with + -al (1) + from Latin terrestris "earthly, of the earth, on land," from terra "earth" (from PIE root *ters- "to dry"). Originally opposed to celestial; natural history sense of "living on land" is attested from 1630s. The noun meaning "a human being, a mortal" is recorded from 1590s.
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extraterrestrial (adj.)

also extra-terrestrial, "occurring or originating outside the Earth," 1812, from extra- + terrestrial. As a noun from 1956.

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*ters- 
Proto-Indo-European root meaning "to dry."

It forms all or part of: inter; Mediterranean; metatarsal; parterre; subterranean; tarsal; tarsus; Tartuffe; terra; terrace; terra-cotta; terrain; terran; terraqueous; terrarium; terrene; terrestrial; terrier; territory; thirst; toast; torrent; torrid; turmeric; tureen.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit tarsayati "dries up;" Avestan tarshu- "dry, solid;" Greek teresesthai "to become or be dry," tersainein "to make dry;" Latin torrere "dry up, parch," terra "earth, land;" Gothic þaursus "dry, barren," Old High German thurri, German dürr, Old English þyrre "dry;" Old English þurstig "thirsty."
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circumpolar (adj.)

"surrounding one of the celestial or terrestrial poles," 1680s in astronomy; 1690s in geography, from circum- "around" + polar.

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terrene (adj.)
"earthly, terrestrial, of or pertaining to the earth," c. 1300, from Anglo-French terreine, Old French terrien, from Latin terrenus "on the earth, earthly," from terra "earth" (from PIE root *ters- "to dry").
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gravity (n.)

c. 1500, "weight, dignity, seriousness, solemnity of deportment or character, importance," from Old French gravité "seriousness, thoughtfulness" (13c.) and directly from Latin gravitatem (nominative gravitas) "weight, heaviness, pressure," from gravis "heavy" (from PIE root *gwere- (1) "heavy"). The scientific sense of "downward acceleration of terrestrial bodies due to gravitation of the Earth" first recorded 1620s.

The words gravity and gravitation have been more or less confounded; but the most careful writers use gravitation for the attracting force, and gravity for the terrestrial phenomenon of weight or downward acceleration which has for its two components the gravitation and the centrifugal force. [Century Dictionary, 1902]
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equator (n.)
late 14c., from Medieval Latin aequator (diei et noctis) "equalizer (of day and night)," agent noun from Latin aequare "make equal" (see equate). When the sun is on the celestial equator, twice annually, day and night are of equal length. Sense of "celestial equator" is earliest, extension to "terrestrial line midway between the poles" first recorded in English 1610s.
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temporal (adj.)
late 14c., "worldly, secular;" also "terrestrial, earthly; temporary, lasting only for a time," from Old French temporal "earthly," and directly from Latin temporalis "of time, denoting time; but for a time, temporary," from tempus (genitive temporis) "time, season, moment, proper time or season," from Proto-Italic *tempos- "stretch, measure," which according to de Vaan is from PIE *temp-os "stretched," from root *ten- "to stretch," the notion being "stretch of time." Related: Temporally.
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pole (n.2)

"northern or southern end of Earth's axis," late 14c., from Old French pole or directly from Latin polus "end of an axis;" also "the sky, the heavens" (a sense sometimes used in English from 16c.), from Greek polos "pivot, axis of a sphere, the sky," from PIE *kwol- "turn round" (PIE *kw- becomes Greek p- before some vowels), from root *kwel- (1) "revolve, move round."

Originally principally in reference to the celestial sphere and the fixed points about which (by the revolution of the Earth) the stars appear to revolve; also sometimes of the terrestrial poles (poles of this world), the two points on the Earth's surface which mark the axis of rotation.

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mercury (n.)

silver-white fluid metallic element, late 14c., from Medieval Latin mercurius, from Latin Mercurius (see Mercury). Prepared in ancient times from cinnabar, it was one of the seven metals (bodies terrestrial) known to the ancients, which were coupled in astrology and alchemy with the seven known heavenly bodies. This one probably was associated with the planet for its mobility. The others were Sun/gold, Moon/silver, Mars/iron, Saturn/lead, Jupiter/tin, Venus/copper.

The Greek name for it was hydrargyros "liquid silver," which gives the element its symbol, Hg. Compare quicksilver, which is its popular name. It has a freezing point of -39° C. The use of the word in reference to temperature or state of the atmosphere (by 1756) is from its use in thermometers and barometers.

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