1540s as a chemical term in reference to alternating vaporization and condensation, from Latin circulatus, past participle of circulare "to form a circle," from circulus "small ring" (see circle (n.)).

Intransitive sense of "to pass about freely, pass from place to place or person to person" is from 1660s; of newspapers from 1885. Of blood, "to flow in a continuous circuit," from 1650s; of persons, "to mingle in a social gathering," from 1863. Related: Circulated; circulating.

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.

also *ker-, Proto-Indo-European root meaning "to turn, bend."

It forms all or part of: arrange; circa; circadian; circle; circuit; circum-; circumcision; circumflex; circumnavigate; circumscribe; circumspect; circumstance; circus; cirque; corona; crepe; crest; crinoline; crisp; crown;  curb; curvature; curve; derange;  flounce (n.) "deep ruffle on the skirt of a dress;" krone; ring (n.1) "circular band;" ranch; range; ranger; rank (n.) "row, line series;" research; recherche; ridge; rink; rucksack; search; shrink.

It is the hypothetical source of/evidence for its existence is provided by: Latin curvus "bent, curved," crispus "curly;" Old Church Slavonic kragu "circle;" perhaps Greek kirkos "ring," koronos "curved;" Old English hring "ring, small circlet."

third letter of the alphabet. Alphabetic writing came to Rome via the southern Etruscan "Caeretan" script, in which gamma was written as a crescent. Early Romans made little use of Greek kappa and used gamma for both the "g" and "k" sounds, the latter more frequently, so that the "k" sound came to be seen as the proper one for gamma. Classical Latin -c-, with only the value "k," passed to Celtic and, via missionary Irish monks, to the Anglo-Saxons. Also see cee.

In some Old English words, before some vowels and in certain positions, -c- had a "ts" sound that was respelled ch- in Middle English by French scribes (chest, cheese, church; see ch). In Old English -k- was known but little used.

Meanwhile, in Old French, many "k" sounds drifted to "ts" and by 13c., "s," but still were written -c-. Thus the 1066 invasion brought to the English language a flood of French and Latin words in which -c- represented "s" (as in cease, ceiling, circle) and a more vigorous use of -k- to distinguish that sound. By 15c. even native English words with -s- were being respelled with -c- for "s" (ice, mice, lice).

In some English words from Italian, the -c- has a "ch" sound (via a sound evolution somewhat like the Old French one). In German, -c- in loanwords was regularized to -k- or -z- (depending on pronunciation) in the international spelling reform of 1901, which was based on the Duden guide of 1880.

As a symbol in the Roman numeral system, "one hundred;" the symbol originally was a Greek theta, but was later reduced in form and understood to stand for centum. In music, it is the name of the keynote of the natural scale, though the exact pitch varied in time and place 18c. and 19c. from 240 vibrations per second to 275; it wasn't entirely regularized (at 261.63) until the adoption of the A440 standard in the 1930s. C-spring as a type of carriage spring is from 1794, so called for its shape.

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.

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.

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.