late 13c., sugre, from Old French sucre "sugar" (12c.), from Medieval Latin succarum, from Arabic sukkar, from Persian shakar, from Sanskrit sharkara "ground or candied sugar," originally "grit, gravel" (cognate with Greek kroke "pebble"). The Arabic word also was borrowed in Italian (zucchero), Spanish (azucar, with the Arabic article), and German (Old High German zucura, German Zucker), and its forms are represented in most European languages (such as Serbian cukar, Polish cukier, Russian sakhar).
Its Old World home was India (Alexander the Great's companions marveled at the "honey without bees") and it remained exotic in Europe until the Arabs began to cultivate it in Sicily and Spain; not until after the Crusades did it begin to rival honey as the West's sweetener. The Spaniards in the West Indies began raising sugar cane in 1506; first grown in Cuba 1523; first cultivated in Brazil 1532. The reason for the -g- in the English word is obscure (OED compares flagon, from French flacon). The pronunciation shift from s- to sh- is probably from the initial long vowel sound syu- (as in sure).
As a type of chemical compound from 1826. Slang "euphemistic substitute for an imprecation" [OED] is attested from 1891. As a term of endearment, first recorded 1930. Sugar-cane is from 1560s. Sugar-maple is from 1731. Sugar loaf was originally a moulded conical mass of refined sugar (early 15c.); now obsolete, but sense extended 17c. to hills, hats, etc. of that shape.