mid-14c., from Old French alchimie (14c.), alquemie (13c.), from Medieval Latin alkimia, from Arabic al-kimiya, from Greek khemeioa (found c.300 C.E. in a decree of Diocletian against "the old writings of the Egyptians"), all meaning "alchemy." Perhaps from an old name for Egypt (Khemia, literally "land of black earth," found in Plutarch), or from Greek khymatos "that which is poured out," from khein "to pour," related to khymos "juice, sap" [Klein, citing W. Muss-Arnolt, calls this folk etymology]. The word seems to have elements of both origins.
The al- is the Arabic definite article, "the." The art and the name were adopted by the Arabs from Alexandrians and thence returned to Europe via Spain. Alchemy was the "chemistry" of the Middle Ages and early modern times; since c.1600 the word has been applied distinctively to the pursuit of the transmutation of baser metals into gold, which, along with the search for the universal solvent and the panacea, were the chief occupations of early chemistry.