Etymology
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unicycle (n.)
1869, American English, from Latin uni- "one" (see uni-) + -cycle, from bicycle (from Greek kyklos "circle, wheel").
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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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cyclamen (n.)

one of a genus of bulbous plants native to southern Europe and western Asia, 1550s, from Medieval Latin cyclamen, from Latin cyclaminos, from Greek kyklaminos, also kyklamis, from kyklos "circle" (from PIE root *kwel- (1) "revolve, move round"). So called apparently in reference to the bulbous shape of the root.

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cyclo- 

before a vowel, cycl-, word-forming element in technical terms meaning "circle, ring, rotation," from Latinized form of Greek kyklos "circle, wheel, ring" (from PIE root *kwel- (1) "revolve, move round"). In organic chemistry it is used in forming chemical names of cyclic compounds.

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encyclical (adj.)
in reference to ecclesiastical letters meant for wide circulation (for example, a letter sent by a pope to all bishops), 1640s, from Late Latin encyclicus, from Latin encyclius, from Greek enkyklios "in a circle, circular," from en "in" (see in) + kyklos "circle" (from PIE root *kwel- (1) "revolve, move round"). As a noun, from 1837.
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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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horizon (n.)
late 14c., orisoun, from Old French orizon (14c., Modern French horizon), earlier orizonte (13c.), from Latin horizontem (nominative horizon), from Greek horizon (kyklos) "bounding (circle)," from horizein "bound, limit, divide, separate," from horos "boundary, landmark, marking stones." The h- was restored in English 17c. in imitation of Latin. Old English used eaggemearc ("eye-mark") for "limit of view, horizon." The apparent horizon is distinguished from the celestial or astronomical horizon.
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encyclopedia (n.)

1530s, "general course of instruction," from Modern Latin encyclopaedia (c. 1500), thought to be a false reading by Latin authors of Greek enkyklios paideia taken as "general education," but literally "training in a circle," i.e. the "circle" of arts and sciences, the essentials of a liberal education; from enkyklios "circular," also "general" (from en "in;" see in + kyklos "circle;" from PIE root *kwel- (1) "revolve, move round") + paideia "education, child-rearing," from pais (genitive paidos) "child" (see pedo-).

Modern sense of "reference work arranged alphabetically" is from 1640s, often applied specifically to the French Encyclopédie ou Dictionnaire raisonné des Sciences, des Arts, et des Métiers (1751-65). Related: Encyclopedist.

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Ku Klux Klan 
1867, American English, originally Kuklux Klan, a made-up name, supposedly from Greek kuklos, kyklos "circle" (see cycle (n.)) + English clan. Originally an organization of former Confederate officers and soldiers, it was put down by the U.S. military in the 1870s. Revived 1915 as a national racist Protestant fraternal organization, it grew to prominence but fractured in the 1930s. It had a smaller national revival 1950s as an anti-civil rights group, later with anti-government leanings. In late 19c. often simply Kuklux.
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