A single word cannot benefit from copyright protection, but a character can. It may be difficult to argue that Anduril and the Palantíri were characters, and even more difficult to argue that the commercial products named after them were substantially similar. Trademark protection may be more applicable, but the Tolkien estate may not have registered (or defended) trademarks for those two names, and if they did it could be argued that a defense company is not confusable with the original material.

On the other hand, maybe both of those companies did secure a license from the Tolkien Estate.