Aben-dul was one of the lost objects.
Meredith receives the sword from skeletal brides in the chamber of decision in the sluagh mound when she asks for weapons. Doyle warns her to touch the sword only with the hand that has the hand of flesh. When she touches it, the hilt changes and images of what the sword can do appear on it.
Meredith uses the sword on Siobhan.
When trapped by King Taranis in her dream, Meredith wishes for a sword and Aben-dul appears in her hand. When she wakes up, she is holding it as well.
In Swallowing Darkness Meredith notes that the sword did not appear to her father, despite him having the hand of flesh as well. In A Shiver of Light, Aben-dul is said to be her father's centuries ago.