Iridescent Siren

A pretty, rarely used Greek name, Thalassa is the ancient personification of the sea, particularly the Mediterranean, who is sometimes considered the mother of Aphrodite. In 1991, a newly discovered moon of Neptune was dubbed Thalassa.

The name of an area in northern Greece, known in the era of Homer's Odyssey as Aeolia, Thessaly makes a spirited and pretty place name. Reminiscent of Tessa, Rosalie, and Thea, the name likely derives from that of an ancient tribe, though the exact meaning isn't known.

Lúthien Tinúviel is an elf princess in J. R. R. Tolkien’s legendarium, who falls in love with a mortal human, Beren, and chooses to become mortal herself rather than to live without him. Tinúviel is a Sindarin name given to her by Beren, meaning "daughter of twilight" and therefore "nightingale".

An elaborate and shiny choice.

More unusual than Tessa, this would make an interesting, meaningful and attractive choice for a third child.

Original Gaelic form of Talulla, often connected with the Choctaw name Tallulah due to the similar sound and spelling.

Mythological water spirit with the more common spelling of Ondine, heroine of an Edith Wharton novel.

A saint's name with a noteworthy literary background, including uses by Shakespeare in Two Gentlemen of Verona and Much Ado About Nothing, by Ben Johnson, Walter Scott, Longfellow, D. H. Lawrence and Neil Gaiman. In real life, her two most well known representatives are writer Ursula Le Guin and actress Ursula Andress. In literature, there is also Ursula Iguaran, a key, long-lived character in Gabriel Garcia Marquez's major work, One Hundred Years of Solitude.

Ursula, while beautiful, still carries a whiff of the Disney sea witch. Perhaps Ursuline smells a bit sweeter?

A pretty, mellifluous name from the Tahitian phrase vai ana o te mato teitei, meaning "water from the cave of the high rock". The Disney heroine Moana is called Vaiana in most European countries, for trademark reasons.