From Tolkien Gateway

An éoherë was the name used by the Men of the Éothéod for a full muster of their armed riders. When Eorl rode from the north to the aid of Gondor, he led an éoherë of some seven thousand horsemen, as well as several hundred mounted archers.[1] The successors of the Éothéod were the Rohirrim, and they continued to use this term. In Théoden's day, some five centuries after the Ride of Eorl, the full éoherë of Rohan was reckoned as one hundred éoreds, or a total of twelve thousand fighting men.[2]

Etymology[edit | edit source]

The word éoherë is Old English (eoh + here), and means (approximately) 'horse-host'. Translated into Númenórean Sindarin, this became the name Rohirrim, the much more common term for the Men of Rohan.[3]