There is only one credible theory for the origin of the name `Ceylon.' One starts with the Pali for the `Place of Jewels,' which is Sihalam goes thro Senendiva (diva for island) and Silandiva, becomes Serendib in Arabic (which incidentally does not mean anything in colloquial New England Arabic) and is contracted to Cilao by the Portuguese and to Zeilan or Ceilan by the Dutch and to Ceylon by the British. Admittedly, the reasoning and linkages are thin.
Horace Walpole wrote the fairy tale named the Three Princes of Serendib in which the heroes have the faculty of making happy and unexpected discoveries by accident. Then a cabal of slnetters used serendipity for the name of their journal but their reports on the serendipitious discovery of the Vallipuram Buddha statue has been anything but happy.
Then there is the Taprobane used by Milton in Paradise Lost, borrowed from the accounts of Alexander the Great's officers who heard reports of the island when in West Asia and from Greek and Ceylonese travellers. Taprobane is supposed to have originated from the `copper colored' (Tamba Vanna in Sanskrit) soil of the place at which Vijaya's retinue landed. They called their capital Tambapanni.
The name (Sri) Lanka was first recorded in the Ramayana and means `resplendent land' in sanskrit. There are other names, including the Tamil Ilanare etc, the Arabic Tenerisim (the isle of delight), the Chinese `Pa-outchow' (the isle of gems), and the `salike' of Ptolemy. Some theologians (Christian and Muslim) thought that Noahs ark came to rest on Serendib. Also when Adam and Eve were thrown out off the garden of Eden for fornication, it was thought appropriate to banish them to this island.
Then there is the Sinbad character in the Arabian Nights supposed to be based on early Arab travellers and there is a description in the Sixth Voyage of Sinbad (`the diamonds are in its rivers and the pearls are in its valleys and Adams peak contains rubies and spice trees' - This must explain the hordes who go there). In 1250 AD, Marco Polo found both men and women of Zeilan nude except for a cloth around the middle part of their bodies and wrote that they ate wine from trees - (must be ra, no?).
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