Arcastar (pron. [arˈkastar]) is the Quenya rendition of the surname Tolkien (German Tollkühn "foolhardy, reckless, desperately brave, rushbold")
J.R.R. Tolkien signed as Arcastar Mondósaresse "Tolkien in Oxford" in a 1968 letter to the producer of the BBC documentary.
The first element seems to be related to the word arauca "swift, rushed" or from the Root (A-RAK).
The second element which can be either *astar or *star must be from stem STAR "stiff, hard"