Brianna is a feminine given name derived from the Celtic name Brian, which itself originated from the Old Celtic word "brig" meaning "high" or "noble." The name is believed to have its roots in Irish and Scottish Gaelic culture, dating back to the Middle Ages.

The name Brianna likely emerged as a feminine form of the traditionally masculine name Brian. One of the earliest recorded instances of the name Brianna can be found in the 16th-century Irish Annals of the Four Masters, where it appears as "Brighid" or "Brighid-Anna."

In Irish mythology, Brighid (or Brigid) was a Celtic goddess associated with spring, fertility, and poetry. Her name was derived from the same Celtic root as Brian and Brianna, further solidifying the connection between the names and their cultural origins.

Throughout history, several notable individuals have borne the name Brianna. One of the earliest recorded examples is Saint Brianna of Tuam, an Irish Catholic saint who lived in the 7th century AD. Another notable figure is Brianna of Brittany (1109-1201), a Breton noblewoman and the daughter of Constance, Duchess of Brittany.

In literature, the name Brianna appears in the works of renowned authors such as Sir Walter Scott and J.R.R. Tolkien. In Scott's novel "The Bride of Lammermoor" (1819), a character named Brianna plays a significant role. Tolkien, known for his detailed world-building, included the name Brianna in his writings, though not as a major character.

Other historical figures named Brianna include Brianna of Saxe-Hildburghausen (1759-1824), a German princess and composer, and Brianna Brewster (1567-1643), a English settler in Plymouth Colony and one of the passengers on the Mayflower.

While the name Brianna has its roots in Celtic culture, it has gained popularity globally in recent centuries. Its melodic sound and association with nobility and strength have contributed to its enduring appeal across various cultures and regions.