Octavia began as the Latin, then Victorian name for an eighth child. While there aren't many eighth children anymore, this ancient Roman name has real possibilities as a substitute for the overused Olivia; recommended for its combination of classical and musical overtones. It was chosen for his daughter by Kevin Sorbo. 
 Octavia has a rich history and literary pedigree. Commonly used in the Roman Imperial family, one first century BC Octavia was the daughter of Claudius, sister of the Emperor Augustus and the second, pre-Cleopatra, wife of Mark Antony (she appears in Shakespeare's Antony and Cleopatra), while another ancient Octavia was the teenage wife of Nero. The British civic reformer Octavia Hill actually was an eighth daughter.
 The name came into the spotlight recently via Octavia Spencer, who won a Best Supporting Actress Oscar for her strong performance in The Help. And Octavia is part of Cinna's prep team for Katniss Everdeen during the 74th and 75th Hunger Games.
 Octavia is also a First Daughter name as the child of President Zachary Taylor.

Octavia

Octavienne

What is so rare as a month named June? October – and November and December – are a lot rarer. Brisk and substantial, they're so much more memorable and modern than April or May. October got its name via being the eighth month in the old Roman calendar. Some related, more feminine variations are Octavia and Ottavia.
 October was chosen by innovative author/editor Dave Eggers and wife Vendela Vida for their daughter. And Neil Gaiman wrote a story personifying the month in his collection Fragile Things entitled October in the Chair.

October

OCTOBRA

Odessa, a Ukrainian port city, was given its name by Catherine the Great, who was inspired by Homer's Odyssey. It would make an original and intriguing choice. 
 Though rare today, Odessa had more U.S. popularity in the past than you might imagine. It actually ranked in the Top 1000 every year from 1880, the year Social Security records began to be kept, through 1956. Then anti-Russian sentiment during the Cold War took it off the table. Michael Chiklis, onetime Commish, has a daughter named Odessa.

Odessa

Odette is the good swan in Tchaikovsky's ballet Swan Lake, a role for which Natalie Portman won an Oscar ---and it would make a particularly soigne, sophisticated yet upbeat choice, unlike some of the more dated other 'ette'-ending names. 
 Odette de Crecy, is the flamboyant wife of Charles Swann in Proust's A la Recherche du Temps Perdu. 
 The name became publicized during World War II via the courageous French Resistance heroine Odette Brailly, who risked her life to supply information to the Allies, was captured by the Germans, and wrote her story which was retold in an eponymous film.
 Actor Mark Ruffalo chose Odette for his daughter. 
 Variant Odetta is associated with the folksinger who was one of the first to go by a single name.
 Odile, who is Odette's evil Swan Lake twin, gives her name a sinuous, sensuous appeal.

Odette

Odette's evil Swan Lake twin -- gives the name a sinuous, sensuous appeal.

Odile

OGYGIA

This chic Ukrainian form of Helen is relatively unknown outside of its native country, but it definitely has international appeal. Olia or Olenka are the usual Ukrainian diminutives, but tomboyish Oli or Leni could work too.

Olena

Mount Olivet is a mountain ridge east of and adjacent to Jerusalem's Old City. It is named for the olive groves that once covered its slopes. Several key events in the life of Jesus, as related in the Gospels, took place on the Mount of Olives, and in the Acts of the Apostles it is described as the place from which Jesus ascended to heaven. This name makes a fresh alternative to Olivia and is worthy of consideration.

Olivet

Olivine

Olwen is a Welsh favorite, the name of a legendary princess in what is believed to have been the earliest Arthurian romance, and in fact one of the first recorded examples of Welsh prose.
 In this tale, Cuthwch and Olwen, the giant's beautiful and gentle daughter Olwen has the magical power to cause white clovers to spring up wherever she walked--an enchanting image. There's a darker side to the story too, in which Olwen's marriage curses her father to die.
 Olwen is a Bronwen alternative for those with a taste for the more unusual. Those who like Olwen might also want to consider such other Welsh girls' names as Anwen, Rhonwen, and Nolwenn.
 24's Xander Berkely and Sarah Clarke used the Olwyn spelling for their daughter.

Olwen

Olwyn is a popular Welsh name that might be an alternative to the more familiar Bronwen or Rhonwen -- though in Wales the female form is usually spelled -wen and the male one -wyn.

Olwyn

Mythological spirit of the waters; spelled Undine, she was an Edith Wharton heroine. 

Ondine

Though this name properly takes an accent over the first e, most Americans would probably have trouble pronouncing it with French elan.
 Ophelie is the title of a Rimbaud poem, Ophelie Davis is a French freestyle skating champ, and Ophelie Winter is a French actress and singerl.

Ophelie

Orabel

Orchid is a hothouse bloom that has not been plucked by many modern baby namers — yet. In the language of flowers, orchids symbolize love, beauty, and sophistication. 
 In a 1926 silent comedy, femme fatale Gloria Swanson played a burlesque chorus girl named Orchid Murphy.

Orchid

Oriana is a dashing medieval name, with a meaning similar to Aurora. At this point, though, Oriana is much more unusual than Aurora and makes a unique choice if you're searching for <a href="https://nameberry.com/list/316/baby-names-that-mean-new-beginnings?all=1">names that mean new beginnings</a> or dawn. Strong and evocative, Oriana also has an admirable literary resume. In medieval tales, she was the beloved of the knight Amadis, she appears in at least three seventeenth century plays, and there is an early Tennyson poem called The Ballad of Oriana. Oriana was also sometimes used to refer to Queen Elizabeth I. Oriana Fallaci was a feminist Italian journalist who interviewed many world leaders in the 1960s, 70s, and 80s.

Oriana

A pretty, feminissima name, more distinctive than Cynthia.  George Bernard Shaw used it for a character in his play The Apple Cart, about which it is said 'Orinthia is a name full of magic for me.'

Orinthia

Cute, nickname-y, and international, à la Romy or Demi. Spelling it Orly turns it into a busy French airport. 

Orli

Orly

Variant of Hortensia, an unusual floral name and the name of a secondary character in Roald Dahl's Matilda.

Ortensia

OSITHE

OSTARA

Softer and more romantic than Octavia, this is a name once used when it wasn't uncommon for families to have eight children. A possible substitute for the epidemically popular Olivia.

Ottavia

Wears long blonde braids, carries a spear, and sings duets with Brunhild.  But variations Ottilie, Ottiline, or Ottoline are both unusual and chic.

Otthild

Ottilie is trending in the UK, where the pronounced T helps the name sound pretty and delicate, rather like Amelie and Elodie. Ottilie is less popular in the US, where many Americans pronounce it as a near-homonym for "oddly".
 
Sweet but stylish, Ottilie was once reserved for the British upper crust, to be spotted among The Telegraph name rankings, rather than in your average school class. However, it has been quickly climbing the charts since 2015, and in 2022, it debuted in the UK Top 100.
 
Rarely seen in the US since the 1880s, Ottilie does have a few cultural references: She is a key character in Goethe's Elective Affinities, Robert Louis Stevenson wrote a poem called To Ottilie, Franz Kafka had a sister named Ottilie, and it is the name of the protagonist in the John Wyndham sci-fi story Random Quest.
 
Probably the best-known Ottilie is the German journalist, abolitionist, and feminist Ottilie Assing, who had a long involvement with fellow abolitionist Frederic Douglass. Others include the Irish Jazz singer, Ottilie Patterson, and Ottilie Rue Sugg, daughter of British influencers, Zoe Sugg and Alfie Deyes. 
 
Popular among Nameberry users, Ottilie is both vintage and playful, with the sweet nickname options of Lottie, Tillie, Otto, and Otter.
 
If the popularity of Ottilie puts you off, or it doesn't sound right in your accent, you could try a variant, such as Ottoline, Ottilia, and Odile, or names with similar sounds and style, such as Odessa, Odette, Romilly, or Coralie.

Ottilie

octobertales's list "O - Girls' Names" of 27 great name ideas: Octavia - Ottilie!