Éored
From the One Wiki to Rule Them All, the Lord of the Rings Encyclopedia.
Éored is the name of a cavalry company of the Rohirrim. During the first three hundred-plus years of Rohan's existence, the term was used widely to describe any significant number of Riders. Under Folcwine King son of Folca, 14th King of the Mark, the military of Rohan was reordered. Under Folcwine, one Éored was made up of 120 riders including their captain. Each Éored was also supposed to comprise one one-hundredth of the whole Muster of Rohan, not including the household of the King.
The changes made by Folcwine continued through the time of the War of the Ring. While the force commanded by Théoden King son of Thengel at the Battle of Pelennor Fields did not number much more than half of 12,000 riders, it was possibly the largest riding of the Rohirrim in history.
A full muster of the Éoreds of Rohan was called an Éoherë. As the tongue of Rohan was modeled after Anglo-Saxon 'Old English', the term Éored is made up of the words 'eoh' (horse) and 'rád' (rides or rode). Likewise Éoherë contains the words 'eoh' and 'herë' (host, army)

