also karat, late 15c., "a measure of the fineness of gold," from Old French carat "measure of the fineness of gold" (14c.), from Italian carato or Medieval Latin carratus, both from Arabic qirat "fruit of the carob tree," also "weight of 4 grains," from Greek keration "carob seed," also the name of a small weight of measure, literally "little horn" diminutive of keras "horn of an animal" (from PIE root *ker- (1) "horn; head").
Carob beans were a standard in the ancient world for weighing small quantities. The Greek measure was the equivalent of the Roman siliqua, which was one-twenty-fourth of a golden solidus of Constantine; hence karat took on a sense of "a proportion of one twenty-fourth, a twenty-fourth part," especially in expressing the fineness of gold when used as jewelry, and thus it became a measure of gold purity (1550s): 18-carat gold is eighteen parts gold, six parts alloy; 14-carat gold is 10/24ths alloy, etc.
As a measure of weight for diamonds or other precious stones, carat is attested from 1570s in English. In U.S., karat is used for "proportion of fine gold in an alloy" and carat for "measure of weight of a precious stone."
gold coin issued by the emperors at Constantinople, c. 1200, from Old French besant (12c.), from Latin byzantius, short for Byzantius nummus "coin of Byzantium." They circulated widely in Europe in the early Middle Ages, when most countries had no gold coins of their own.
c. 1300 (mid-13c. in Anglo-Latin), "wreath of flowers," also "crown of gold or silver," from Old French garlande "garland," probably from a Frankish frequentative form of *weron "adorn, bedeck," from *wiara-, *weara- "wire" (on the notion of "ornament of refined gold," properly "of twisted gold wire"), from Proto-Germanic *wira-, *wera-, suffixed form of PIE root *wei- "to turn, twist." Compare Middle High German wieren "adorn, bedeck." The word is found in many forms in the Romanic language, such as Old Spanish guarlanda, French guirlande, Italian ghirlanda, Portuguese grinalda.
type of coin, c. 1300, from Old French florin, from Italian fiorino, from fiore "flower," from Latin florem "flower" (from PIE root *bhel- (3) "to thrive, bloom"). The 13c. gold Florentine coin was stamped on the obverse with the image of a lily, the symbol of the city. As the name of an English gold coin, from late 15c.
French coin, late 14c., frank, from French franc; a name said to have been given because Medieval Latin Francorum Rex, "King of the Franks" (see Frank), was inscribed on gold coins first made during the reign of Jean le Bon (1350-64). Used of different gold and silver coins over the years; as the name of an official monetary unit of France from 1795.
1854, spelling variant of carat (q.v.). In U.S., karat is used for "proportion of fine gold in an alloy" and carat for "measure of weight of a precious stone."