The first legend concerns Dian Cecht's powers as a smith and craftsman. Nuada, once the leader of the Tuatha De Danaan, had gotten himself into a bit of a bind, in that he had lost his arm in battle. This serious wound had disqualified Nuada from his position as king, and in his absence, the unsavory Bres had stepped in to rule the Tuatha De. Unfortunately, no one was pleased with this change of leadership (except maybe Bres himself), so Dian Cecht created an arm of silver to make Nuada "whole" again. With his new limb, Nuada could once more rule his people, thanks to the industrious Dian Cecht.
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Dictionary of Celtic Mythology
This book is a great source for information about Celtic mythology! Described as both a "who's who" and a "what's what", this reference book features entries on the important gods, heroes, and other characters from Celtic myth and legend. And there is a good entry on the god Dian Cecht.