It turns out that a Greek poetess Sappho, who lived in ancient Greece in 7th century BC wrote poetry about love, some of it addressed to women. Sappho lived on the Lesbos island that is located in the Aegean Sea.

Although the inhabitants of Lesbos are properly referred to as "Lesviots" or "Lesvonians", in many translations from classical Greek to English they're called "Lesbians". Apparently they're not so happy about this connection:

In recent years this has often made Lesbos the destination of cruises and other vacations for lesbians, despite the disapproval of conservative Lesviot authorities, with some cruise ships being denied permission to dock.
-- Wikipedia

By the way, deriving from Sappho's name, Sapphic is a rare synonim to "Lesbian" in the sexual context.