The ushaan-tor is a curved Andorian tool originally used to mine ice, and the weapon of the ushaan, the Andorian honor duel.
In the ushaan, combatants are tethered together and fight with ushaan-tors until one dies or yields. In 2154 Shran invoked the duel against the Tellarite he held responsible for the death of his companion Talas, and Captain Archer took the Tellarite's place to preserve the fragile coalition working against the Romulans.
Rather than kill Shran, Archer severed one of his antennae, which left him unable to continue. The antenna grew back in time, and the outcome strengthened the respect between the two men.