What is "eotheod"

In the fictional world of J. R. R. Tolkien, the Éothéod were a group of Northmen who became the ancestors of the Rohirrim. The word, meaning "horse people", is a compound of the Old English words éoh ("horse" or "war horse") and théod ("people", "race"); it is cognate with Old Norse jóþjóð ("horse people"). Tolkien used the word to refer also to the land they occupied in the Vales of Anduin.