"... a small, bent black rod, perhaps an inch in diameter, that had a strangely dull look."
It is a weapon that can be used for stunning or killing someone from the distance of a hundred paces.
Asne affirmed that the rod was a 'gift' from Moghedien but, from a comment given by another Black Sister, Asne found the rod searching in the Forsaken bedroom in Samara, after Moghedien was absent for a long time and never returned to them, because in fact she was captured by Nynaeve in Salidar. Later Asne used it in Caemlyn to stun Elayne, Sareitha, Careane and Vandene at the house on Full Moon Street.
How this ter'angreal is activated is unclear. When it is in use it is not detected by channelers, Asne affirmed that the rod can kill a men surrounded by Aes Sedai without any of them able to feel from where the attack is coming.