Noun

1. That which braces, binds, or makes firm; a band or bandage.
2. A covering to protect the arm of the bowman from the vibration of the string.
   • 1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page 34:

     To prevent the bow string from hanging on the left arm, it is covered with a piece of smooth leather, fastened on the outside of the arm, this is called a bracer.

3. Armor for the forearm; a brassart.
4. A medicine, as an astringent or a tonic, which gives tension or tone to any part of the body.