Board Thread:General Discussion/@comment-26394456-20150714132009/@comment-26394456-20150721173337

According to the Mor'du page on the Pixar Wikia, the name Mor'du (we've been spelling it wrong) may come from the Gaelic words "mor," meaning giant, and "dubh," meaning black. This could be a reference to his appearance. Also, it may come from the word for death in Latin, "mortus." There is also a french word "Mordu" that means bitten. This might be a reference to him, biting off Mirida's father's leg.

According to Behind the Name, Mordred comes from the Welsh word, "medraunt," which means uncertain. Even though I'm no expert, I believe Mordred could have come from the Latin word for death.