Etymology
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circulation (n.)

mid-15c., circulacioun, in alchemy, "process of changing something from one element into another," from Latin circulationem (nominative circulatio), noun of action from past-participle stem of circulare "to form a circle," from circulus "small ring" (see circle (n.)).

Of blood, "act of moving so that it returns and begins again," first by William Harvey, 1620s. Meaning "act or state of being distributed" is from 1680s; that of "extent to which a thing circulates" (of periodical publications) is from 1847.

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epicycle (n.)
"small circle moving on or around another circle," late 14c., from Late Latin epicyclus, from Greek epikyklos, from epi (see epi-) + kyklos "circle, wheel, circular motion, cycle of events" (from PIE root *kwel- (1) "revolve, move round"). Related: Epicyclic.
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cyclic (adj.)

1794, "pertaining to or moving in a cycle or circle," from French cyclique (16c.), from Latin cyclicus, from Greek kyklikos "moving in a circle," from kyklos "circle, wheel, any circular body, circular motion, cycle of events" (see cycle (n.)). Sense of "connected to a literary cycle" is by 1822.

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gyrus (n.)
convolution between grooves of the brain, 1827, from Latin gyrus "circle, circuit, career," from Greek gyros "a ring, circle" (see gyre (n.)).
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mandala (n.)

symbolic magic circle used by Buddhists in meditation, 1859, from Sanskrit mandala "disc, circle." Adopted 20c. in Jungian psychology as a symbol of unity of the self and completeness.

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gyromancy (n.)
1550s, method of divination said to have been practiced by a person walking in a circle marked with characters or signs till he fell from dizziness, the inference being drawn from the place in the circle at which he fell; from Medieval Latin gyromantia, from Greek gyyros "circle" (see gyro- (n.)) + manteia "divination, oracle" (see -mancy).
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cyclone (n.)

1848, "extensive storm characterized by the revolution of air around a calm center in which the wind blows spirally around the center," coined by British East India Company official Henry Piddington to describe the devastating storm of December 1789 in Coringa, India; irregularly formed from a Latinized form of Greek kyklon "moving in a circle, whirling around," present participle of kykloun "move in a circle, whirl," from kyklos "circle" (from PIE root *kwel- (1) "revolve, move round"). Applied to tornadoes from 1856.

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radian (n.)
"angle subtended at the center of a circle by an arc equal in length to the radius," 1879, from radius.
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coterie (n.)

"exclusive set or circle of persons who are in the habit of meeting and socializing, a clique," 1738, from French coterie "circle of acquaintances," originally an organization of peasants holding land from a feudal lord (14c.), from cotier "tenant of a cote" (see cottage).

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esoterica (n.)
by 1807, from Latinized plural of Greek esoterikos "belonging to an inner circle, pertaining to those within" (see esoteric).
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