Anakin: "Anakim" is one of the several names in the Old Testament for a race of giants, "the sons of the gods [who] lay with the daughters of men" [Genesis 6:4]; "Anakim" is plural. this may refer to Anakin's great height, if Vader's size was not installed with the armor. ( http://www-atdp.berkeley.edu/1623/students/kimberly/names.html )
But I read (can't remember where) that
George Lucas, made the name up for his character in the
Star Wars novels....
Hope this helps,
Magia