Etymology
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circumference (n.)

"line that bounds a circle" (loosely, "any boundary line"), late 14c., from Latin circumferentia, neuter plural of circumferens, present participle of circumferre "to lead around, take around, carry around," from circum "around" (see circum-) + ferre "to carry," from PIE root *bher- (1) "to carry," also "to bear children." A loan-translation of Greek periphereia "periphery, the line round a circular body," literally "a carrying round" (see periphery). Related: Circumferential.

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*bher- (1)

Proto-Indo-European root meaning "to carry," also "to bear children."

It forms all or part of: Aberdeen; amphora; anaphora; aquifer; auriferous; bairn; barrow (n.1) "frame for carrying a load;" bear (v.); bearing; Berenice; bier; birth; bring; burden (n.1) "a load;" carboniferous; Christopher; chromatophore; circumference; confer; conference; conifer; cumber; cumbersome; defer (v.2) "yield;" differ; difference; differentiate; efferent; esophagus; euphoria; ferret; fertile; Foraminifera; forbear (v.); fossiliferous; furtive; indifferent; infer; Inverness; Lucifer; metaphor; odoriferous; offer; opprobrium; overbear; paraphernalia; periphery; pestiferous; pheromone; phoresy; phosphorus; Porifera; prefer; proffer; proliferation; pyrophoric; refer; reference; semaphore; somniferous; splendiferous; suffer; transfer; vociferate; vociferous.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bharati "he carries, brings," bhrtih "a bringing, maintenance;" Avestan baraiti "carries;" Old Persian barantiy "they carry;" Armenian berem "I carry;" Greek pherein "to carry," pherne "dowry;" Latin ferre "to bear, carry," fors (genitive fortis) "chance, luck," perhaps fur "a thief;" Old Irish beru/berim "I catch, I bring forth," beirid "to carry;" Old Welsh beryt "to flow;" Gothic bairan "to carry;" Old English and Old High German beran, Old Norse bera "barrow;" Old Church Slavonic birati "to take;" Russian brat' "to take," bremya "a burden," beremennaya "pregnant."

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perimeter (n.)

early 15c., perimetre, "circumference, outer boundary, or border of a figure or surface," from Latin perimetros, from Greek perimetron "circumference," from peri "around, about" (see peri-) + metron "measure" (from PIE root *me- (2) "to measure"). Military sense of "boundary of a defended position" is attested by 1943. Related: Perimetric; perimetrical.

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periphery (n.)

late 14c., periferie, "atmosphere around the earth," from Old French periferie (Modern French périphérie) and directly from Medieval Latin periferia, from Late Latin peripheria, from Greek peripheria "circumference, outer surface, line round a circular body," literally "a carrying around," from peripheres "rounded, moving round, revolving," peripherein "carry or move round," from peri "round about" (see peri-) + pherein "to carry," from PIE root *bher- (1) "to carry."

In geometry, the meaning "outside boundary of a closed figure," especially the circumference of a circle, is attested in English from 1570s; the general sense of "boundary, surface" is from 1660s.

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radial (adj.)

c. 1400, "of or like a ray or radius," from Medieval Latin radialis, from Latin radius "shaft, rod; spoke of a wheel; beam of light" (see radius). Meaning "arranged like the radii of a circle" is by 1750. As a noun, "a radiating or radial part," by 1872. As a type of tire, attested from 1965, short for radial-ply (tire), so called because the cords run at right angles to the circumference. Related: Radially.

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pi (n.)

Greek letter corresponding to the Roman P, from Phoenician, literally "little mouth." As the name of the mathematical constant for the ratio of the circumference of a circle to the diameter, from 1841 in English, used in Latin 1748 by Swiss mathematician Leonhard Euler (1707-1783), as an abbreviation of Greek periphereia "periphery." For the printer's term for mixed type (often spelled pi), see pie (3).

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around (adv.)

c. 1300, "in circumference, in a circle, on every side," from phrase on round; see a- (1) + round (adj.). Rare before 1600. In sense of "here and there with no fixed direction" it is attested from 1776 in American English (British English prefers about). As a preposition, "on or along a circuit," late 14c.; "on all sides, encircling, about" 1660s; of time, by 1873. To have been around "gained worldly experience" is from 1927, U.S. colloquial; to get around to it is from 1864.

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ambit (n.)
late 14c., "space surrounding a building or town; precinct;" 1590s, "a circuit;" from Latin ambitus "a going round, a circuit, circumference," noun use of past participle of ambire "to go around, go about," from amb- "around" (from PIE root *ambhi- "around") + ire "go" (from PIE root *ei- "to go").
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paddle-wheel (n.)

also paddlewheel, "wheel provided with boards or floats around its circumference, for use in moving water," 1680s, so called by its inventor, but the word was not in common use until 1805 and the rise of the steamboat with a side-mounted paddle-wheel turned by steam power for the propulsion of the vessel, from paddle (n.) + wheel (n.).

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tour (n.)
c. 1300, "a turn, a shift on duty," from Old French tor, tourn, tourn "a turn, trick, round, circuit, circumference," from torner, tourner "to turn" (see turn (v.)). Sense of "a continued ramble or excursion" is from 1640s. Tour de France as a bicycle race is recorded in English from 1916 (Tour de France Cycliste), distinguished from a motorcar race of the same name. The Grand Tour, a journey through France, Germany, Switzerland, and Italy formerly was the finishing touch in the education of a gentleman.
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