Well, I've since moved on to finishing the essay but the name stays with me. I'm not enough of a linguist to understand how to break the words down. I believe "tyrn" is the plural of "toron, torn" (brother). "Gorthad" seems to be a combination of two words, the second one possibly a variant of "atta" (two) or "adu" (double). "Gor" is the hard part. There are several possible candidates, I think, which could mean "vigor, vigour", "dread, horror", "round,rounded", etc.

Has anyone else tried to decipher these words? Have any of you heard of any attempts to do so? My Web searches have been unsuccessful.

I'm not sure if Tolkien provided any clues in the book to help in unravelling the meaning of the phrase. There are two mysterious stones which Frodo passes through just before he climbs the hill and is taken by the Barrow-wight. But the name seems to be applied to the entire region of hills (downs) between the Old Forest and the Greenway. And the hills don't extend all the way to the Great Road, but rather are cut off some miles south of it. A dike and wall at the northern edge of the hills marked the boundary between Arthedain and Cardolan (and the wall is on the northern side of the dike, so it was apparently built by Arthedain).

However, the name "Tyrn Gorthad" might extend further back than the days of the Dunadan kingdom. The Edain had pastured their flocks in those hills during the First Age, and presumably Edainic peoples continued to live in the throughout the Second Age (or at least until the War of the Elves and Sauron). The Kings of Arnor (and presumably Cardolan) were buried in the hills after Elendil's return (although Valandil would have to have been the first of these to be interred there).
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