Like the name "Brazil", the word "Antilles" dates from a period anterior to the discovery of the New World, "Antilia[?]" being one of those mysterious lands which figured on the medieval charts sometimes as an archipelago, sometimes as continuous land of greater or lesser extent, constantly fluctuating in mid-ocean between the Canaries and East India. But it came at last to be identified with the lands discovered by Columbus.
Later, when Columbus's Indian territories emerged as a vast archipelago enclosing the Caribbean Sea and the Gulf of Mexico, "Antilia" assumed its present plural form, Antilles, which collectively applied to the whole of this archipelago. A distinction is made between the "Greater Antilles[?]", including Cuba, Jamaica, Haiti, and Puerto Rico; and the "Lesser Antilles" (the remainder of the islands).
The concept survives in the name of the Netherlands Antilles.
Original text after the 1911 Encyclopaedia Britannica