c. 1500, "very small kind of seedless blackish raisin or dried grape, used in cookery and confections," a shortening of raysyn of Curans (late 14c.) "raisins of Corinth," with the -s- mistaken for a plural inflection. From Anglo-French reisin de Corauntz. The raisins were exported from southern Greece.
In 1570s the word was applied to the small round red or black berry of an unrelated Northern European plant (genus Ribes), then lately introduced in England, on its resemblance to the raisins. It later was applied to plants having similar fruit in America and Australia.
1785, in reference to a type of flower cluster, from Latin racemus "a cluster of grapes" (see raisin). In Middle English, "a raisin or currant" (late 14c.).