In the novels it is always represented by the Mercian dialect of Anglo-Saxon. This is because Tolkien saw the relationship between Rohirric and the Common Speech to be the same as that of Anglo-Saxon and English, which was used to represent Westron. Only a few actual Rohirric words are given by Tolkien: kûd-dûkan, an old word meaning "hole-dweller" which led to kuduk, the name the Hobbits had for themselves. Even these terms were translated in the book: "hobbit" is said to derive from the Anglo-Saxon construction "hol-bytla", or hole-builder.
All names beginning with Éo– are actually names beginning with Lô– or Loh–, but the real forms of Éomer, Éowyn etc. are not given. Only one proper name is given, that of Théoden: the actual form was Tûrac, which implies that Rohirric had adopted the Sindarin element "tur–" also present in names like Turgon, with meaning power/mastery (i.e. King).