The name Rhonwen is a girl's name of Welsh origin meaning "slender, fair". Rhonwen and is often added to lists like British Girl Names and discussed in our forums with posts like "Hunt for our favourite girl names (Alphabet-wise)".
From the experts:
The delicate and haunting Welsh Rhonwen is still a rarity in the U.S., where her English version Rowena is better known, but would be a lovely choice for any parent in search of a name that was both unusual and traditional, classically feminine yet strong.
Though Irish names have long been popular in America, Welsh names are just beginning to be noticed and we see them as a wave of the future. In medieval Welsh poetry, Rhonwen is called "the Mother of the English Nation," and Rhonwen Baganes was a heroine of Welsh folklore. A soft and gentle name, Rhonwen's meaning—slender and fair–evokes the image of a lovely, light-haired girl. Other appealing 'wen' choices include Aelwen, Arianwen, Branwen, Bronwen. Gwendolen, Olwen and Tanwen. Just don't be tempted to change the 'wen' to 'wyn', which would transform it into a male name.