Sidonia von Bork (1860) Sir Edward Coley Burne-Jones
The more elegant, rarer version of Sidony and Sidonie, is the mysterious and strong Sidonia. Pronounced sih-DOH-nee-ah and sid-OHN-ya, the name means "of Sidon," the ancient Phoenician city. From the masculine Sidonius, and sounding so close to Sydney, this name does ooze a mystical place-name vibe. Today, the city would be equivalent to Saida in Lebanon.
The 5th century Saint Sidonius Apollinaris was a bishop of Clermont, but there was later a 7th century Saint Sidonius. For women, there was a legend of Saint Sidonia clutching the robe of Jesus, and another Saint Sidonia who was the former's descendant.
Sidonia the Sorceress was a well known tale that inspired Pre-Raphaelite artists such as Sir Edward Coley Burne-Jones, as in the image above. One of the versions of this story was translated by Oscar Wilde's mother Francesca Speranza Lady Wilde. Sidonia in the story, and portrayed in the painting, is a wicked and beautiful woman who hurt men with enchantments. Sidonia von Bork/Borcke, born 1548, was a real life Pomeranian noblewoman executed for witchcraft, the inspiration for Sidonia the Sorceress. Although the noblewoman was living in a convent, she was accused of witchcraft because people needed someone to blame for the deaths of a few noblemen and the public had superstitions about the Duchy of Pomerania.
Sidonie of Saxony, born 1518, was another woman accused of witchcraft. She was a princess of the House of Wettin. She had a very unhappy marriage, and even though her husband presented "evidence," she was acquitted of all charges.
In fiction, the Knights of Sidonia is a Japanese comic, and Farewell Sidonia was a novel written by Erich Hackl in 1989. In real life the Order of Sidonia was a chivalric order for women put in place by the Kingdom of Saxony. Sidonia Hedwig Zäunemann was a German poet Laureate at age 24. Medina-Sidonia is an ancient Andalusian city (first Phoenician) in Spain.
White Pages claims there are currently about 406 people in the U.S. named Sidonia. Unlike Sydney, which ranked at #78 in 2012, and Sidney at #831, Sidonia was most popular in 1923 with only 13 births for the year. She was last used in 2007 with only 6 births for the year. Sidonie is also very rare - in 2012 it was only used 7 times, and it does not have as long of a history in the U.S. as Sidonia.
Nickname options include (but are not limited to) Sid, Sidney/Sidnie, and Sonia.