Brynne is related to Welsh bryn, meaning hill or mound.
Brynne is an elegantly spare name drawn from the Welsh landscape itself. It derives from the Welsh word "bryn," meaning hill — one of those geographical terms so woven into the Celtic languages that it appears constantly in Welsh place names: Brynmawr, Brynmenyn, hundreds of hills named and renamed across the rain-green valleys of Wales. To name a child Bryn or Brynne is, in a sense, to name her after the land, after that quality of rising above and looking out from elevation.
There is a nobility in this etymology that does not depend on aristocratic pedigree but on the older, more democratic grandeur of topography. The spelling "Brynne" — with the added "e" — is predominantly an American and Canadian development, a feminizing flourish added to the more traditionally unisex Welsh original. In Wales itself, Bryn is used for both boys and girls and carries its geographical meaning without any gendered connotation.
The double-n spelling that sometimes appears is a way of hinting at that Welsh phonology, where double consonants signal a specific vowel quality. Literary and cultural associations are pleasingly quiet for this name — it has not been heavily colonized by any single famous bearer or fictional character, which means it arrives in a child's life relatively free of pre-loaded associations. It gained modest traction in North America during the 1990s and 2000s as Welsh and Celtic names enjoyed a broader revival. Today it reads as quietly sophisticated: short, strong, distinctly feminine in its dressed-up American spelling, and connected to something ancient and elemental.