The girl's name Castalia (Κασταλια) is pronounced kah-STAH-lia, and/or KASS-tah-lee-uh. She was a nymph, daughter of the river Achelous, who gave her name to the Castalian Spring near Delphi, Greece - home of the prophetic Oracle of Delphi. According to some legends she married the King of Delphi (possibly King Delphus who gave his name to the city) and had a son with him, who was named Castalius. According to other legends, she became the Castalian Spring itself by diving into the fountain at the foot of Mount Parnassus after being pursued romantically by the god Apollo. Now she is a muse who inspires poetic genius to those who touch her waters, and the other muses are sometimes called Castalides, or it is used as their surname or collective name, because they are associated with this spring. 'Castalian' is now a word, meaning "pertaining to Castalia, fountain of Parnassus."
Virginia Woolf used this name for a character in A Society, German writer Herman Hesse used it as a Utopian location in his series The Glass Bead. Castalia House is a Finnish publisher. Caria castalia, also known as the Green Mantle, is a species of butterfly. Castalius is also a butterfly genus with four species. Castalia odorata is one of the names of the American white water lily aka white pond lily aka Nymphaea odorata. 4769 Castalia is a near-earth asteroid. There are a few U.S. towns named Castalia. Castalia Blue Hole, located in Castalia, Ohio, is a deep fresh water pond with a vibrant blue color that draws in tourists for its incredible beauty. The Castalian Band was the name of a group of late 1500s court poets that were Scottish Jacobean in the court of James VI. They took the name from the idea that the Castalian Spring gave the gift of poetic inspiration.
Castalia's likely meaning is "to sew" or "sew together" from Greek kassuo. Kassotis was the place where the river Achelous first formed into a spring at the top of Mount Parnassos, and in some accounts Kassotis is her own being separate from Kastalia, therefore she was a nymph whose water gave the Delphi Oracle her legendary prophetic powers. Kastalia, as a separate location and a nymph with her own myth, was the point at which the spring reappeared below - and the two were "sewn together." Kastalia might have just a slightly different etymology from Kassotis, though. It's entirely possible the different ending comes from halos, and the meaning would then be "sewing needle." But let's stick with "sewn together" until further research is done. Some would have you believe the etymology of the name is "sacred fountain of the muses," which is careless and lazy, because that is just a modern description of the place, not the name itself. Many have suggested Castalia is from Latin castus, meaning "chaste," but this is a Greek origin name - not Latin. At least one source suggests the meaning is "spring; source," with reference to a mountain spring, from Old European but not PIE. The SSA does not have record of this name, but White Pages reports about 67 people with this name living in the U.S.