Dawn

Dawn is the ancestral sword of House Dayne. The sword's bearer is a knight of the family, who bears the title of "the Sword of the Morning".

During the reign of the Mad King, Ser Arthur Dayne of the Kingsguard bore Dawn.

Season 4
Dawn is mentioned in Ser Arthur Dayne's entry in the Book of Brothers.

In the books
In the A Song of Ice and Fire novels, Dawn was forged from the metal of a fallen star. Its blade is as pale as milkglass and is said to be just as sharp as Valyrian steel.

According to George R.R. Martin, Dawn remains at Starfall castle during the War of the Five Kings, because no new warrior of House Dayne has yet proven himself worthy to wield it as a new Sword of the Morning.