Why was Sri Lanka known as serendib?

The ancient Greeks and Romans called Sri Lanka "Taprobane" or "Serendib." The name "Serendib" comes from the Sanskrit word "Sinhaladvipa," which means "the island of the Sinhalese people." The name "Serendib" was also used by Arab and Persian traders who visited the island. The name "Sri Lanka" is derived from the Sanskrit word "Sihaladvipa," meaning "the resplendent island."