Definition of "couter"

Helmets should be started in 10 or 12 gauge, couters and knees in 14 gauge.

2000, Brian Price, Techniques of Medieval Armour Reproduction: The 14th Century

Full rerebraces enclosed the entire upper arm, with a hinge to allow them to be opened and straps and buckles to fasten them shut. Below the rerebrace was the elbow piece called a couter. The couter was small and conical, often shaped to a point, with a wing on the outer side as on the poleine, and with buckled straps to secure the arm harness snugly to the arm.

2009, Jeffrey L. Forgeng, Will McLean, Daily Life in Chaucer's England, page 169

For example, it is unlikely that the right couter could be damaged or that it could be hit at all if the jouster had a large protective vamplate in place on his lance, though by the same token the folio of the Inventario iluminado on which Real Armeria harness A16 is illustrated (chapter 2, fig. 54) includes six vamplates of varying shapes and sizes for the joust royal so there is no guarantee that such capacious vamplates were used in each and every joust.

2010, Noel Fallows, Jousting in Medieval and Renaissance Iberia, page 205

In some cases, the fashion for a short-sleeved hauberk similar to the earlier twelfth-century design allowed the lower canon to be worn beneath the mail, whilst the rerebrace, couter and spaudler still remained over the mail.

2013, Paul F Walker, History of Armour 1100-1700