Meaning "string of a musical instrument" is from 1660s (earlier this was cord). The geometry sense "straight line intersecting a curve" is from 1550s; figurative meaning "feeling, emotion" first attested 1784, from the notion of the heart or mind as a stringed instrument.
mid-15c., "cord, lace, or ribbon of fine material worn as an ornament or token of victory," from Old French cordon "ribbon, cord," diminutive of corde "cord" (see cord). Military sense of "a line of troops or military posts guarding a place" is by 1758.
The original sense is preserved in cordon bleu (1727) "the highest distinction," literally "blue ribbon," for the sky-blue ribbon worn by the old French order of Knights-grand-cross of the Holy Ghost (the highest order of chivalry under the Bourbons). Extended figuratively to other persons of distinction, especially, jocularly, to a first-rate cook.
Cordon sanitaire (1857) is French, a line of troops or military posts set around an infected district to keep the disease from spreading.
"thick, cotton stuff with a corded or ridged surface," 1774, probably from cord + obsolete 17c. duroy, name of a coarse fabric made in England, which is of unknown origin. Folk etymology is from *corde du roi "the king's cord," but this is not attested in French, where the term for the cloth was velours à côtes. As an adjective from 1789. Applied in U.S. to a road of logs across swampy ground (1780s) on similarity of appearance.
CORDUROY ROAD. A road or causeway constructed with logs laid together over swamps or marshy places. When properly finished earth is thrown between them by which the road is made smooth; but in newly settled parts of the United States they are often left uncovered, and hence are extremely rough and bad to pass over with a carriage. Sometimes they extend many miles. They derive their name from their resemblance to a species of ribbed velvet, called corduroy. [Bartlett]
"related notes in music," 1590s, ultimately a shortening of accord (or borrowed from a similar development in French) and influenced by corde "string of a musical instrument" (c. 1300), which is Latin chorda "catgut, a string" of a musical instrument (see cord (n.)).
English cord as a shortening of accord is attested from mid-14c.; cord meaning "music" is attested in English from late 14c. The spelling with an -h- is first recorded c. 1600, from further confusion with chord (n.2) and perhaps also classical correction. Originally two notes sounded simultaneously; of three or more from 18c.
*gherə-, Proto-Indo-European root meaning "gut, entrail."
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit hira "vein; band;" Latin hernia "rupture;" Greek khorde "intestine, gut-string;" Lithuanian žarna "guts, leather bag;" Old English gearn, Old High German garn "yarn" (originally made of dried gut), Old Norse gorn "gut."
"division of the animal kingdom including the true vertebrates," 1880, Modern Latin, from neuter plural of Latin chordatus "having a (spinal) cord," from chorda "cord, string" (from PIE root *ghere- "gut, entrail").
"pertaining to the nape of the neck or spinal cord," 1835, medical Latin, from nucha "spinal cord" (c. 1400), from Medieval Latin nucha, from Arabic nukha "spinal marrow."
1711, "rent made by ripping or tearing," from rip (v.). The U.S. colloquial meaning "a rapid rush" is by 1855. The parachutist's rip cord (1906) originally was a device in ballooning to open a panel and release the hot air (1868, also ripping-cord).