Welsh: meaning is unclear, though I have seen it defined as "Silver Tongue" or "Silver-Grey." While the first part may be correct--"Silver"--the second doesn't; the words for "tongue" and "grey" are not found containing "awn."
1. Arawn is the king of Annwfn/Annwn in The Mabinogion story "Pwyll Pendeuc Dyfed." His enemy is Hafgan--"Summer White." He has a pack of hunting dogs with white bodies and red ears--the Cwn Annwn of the Wild Hunt. When the young chieftain Pwyll foolishly tries to hunt Arawn's otherworld prey, Arawn has Pwyll switch places and fight Hafgan. In return, Arawn gave Pwyll magic swine from the Otherworld, which were later passed down to Pryderi.
There is some debate as to whether Arawn is simply a title; in the poem "Cad Goddeu," Arawn is identified with Bran, who later becomes the Fisher King.
2. The lord of Annuvin and king of evil in The Chronicals of Prydain series. He is the enemy of the Children of Don and lord of the Cauldron Born.