Contrary to the previous poster's comment, Arwen does not mean "evening star." Evenstar was the surname of Tolkien's character Arwen, not the meaning of her name. In Sindarin, the "ar" prefix means "noble, " and "-wen" means "maiden," so the BtN definition is correct.
-- Anonymous User 4/21/2006
The name is of Welsh origin, "ar" meaning noble and "wen" meaning maiden in the Welsh language. It is not, as now commonly believed, a fictonal name.
You are mistaken in thinking that the name has an historical origin in Wales. Much like Eowyn, it is a fictional creation of Tolkien's that draws upon and bears a deliberate resemblance to real Dark Age names.
Means "noble maiden" in the fictional Quenya Elvish tongue.
Arwen wouldn't sound out of place in real-life England or Wales in the Middle Ages, however, as many Old English and Brythonic names have a similar form, for example Ædwen and Ceridwen. Interestingly, Ar = 'Mercy' and Wen = 'Hope' in OE.
First of all, Arwen Undomiel is Sindarin for 'noble maiden' 'evenstar.' Tolkien based his languages off of many 'real' languages, especially Welsh and Finnish.
The name Arwen is NOT made up from Sindarin. JRR Tolkien did create a Sindarin meaning for the name, but he got the name from Old Welsh. In Welsh, Arwen means "fair" or "fine" and has a masculine form - Arwyn.