Avonna is likely a modern English coinage, probably influenced by Ava and names ending in -onna.
Avonna sits at a lyrical crossroads of several naming traditions, its exact origin deliberately soft and open. Its most likely linguistic ancestor is the Celtic root "abona" or "afon," the Brittonic and Welsh word for river — the same root that gave England the River Avon, Shakespeare's famous Avon, and the place name Avon itself. The River Avon appears so many times across Britain precisely because it was once simply what local Celtic speakers called any river: the water, the flowing one.
There is something quietly elemental about a name that traces back to the concept of a river. Avonna may also be understood as a feminine elaboration in the tradition of Yvonne, the French name derived from the Germanic element "iv" (yew tree), which arrived in England with the Normans and produced a cluster of related feminine forms. The added syllable and feminine "-a" ending are characteristic of naming creativity in mid-twentieth-century America, where parents developed new feminine forms by extending and softening existing sounds.
The Avon cosmetics company, founded in 1886 and named after the Stratford-upon-Avon birthplace of Shakespeare, lent the root a glamorous, aspirational resonance for much of the twentieth century — the Avon lady being a recognizable figure of door-to-door independence. Avonna carries all of these streams: the ancient flow of Celtic rivers, the gentle femininity of French naming, and a distinctly American creative spirit.