I was reading an answer to a question and in the answer it was mentioned that:
[The Witch-king] had been shaken by the fire of Gandalf, and began to perceive that the mission on which Sauron had sent him was one of great peril to himself both by the way, and on his return to his Master (if unsuccessful); and he had been doing ill, so far achieving nothing save rousing the power of the Wise and directing them to the Ring. But above all the timid and terrified Bearer had resisted him, had dared to strike at him with an enchanted sword made by his enemies long ago for his destruction. Narrowly it had missed him. How he had come by it — save in the Barrows of Cardolan. Then he was in some way mightier than the B[arrow]-wight; and he called on Elbereth, a name of terror to the Nazgûl. He was then in league with the High Elves of the Havens.
From Tolkien's The Hunt for the Ring essay, reproduced in The Lord of the Rings: A Readers's Companion
I wanted to know the story behind the bold lines. I do not have access to the books and the LOTR Wiki was of no help in this regard.