I cannot fathom the fiery letters

I’m re-reading The Lord of the Rings for the umpteenth time, and it is such a joy to re-immerse myself in Tolkien’s language–lyrical, visual, and sometimes beyond my ken. In particular, the use of archaic units of measurement has been tripping me up, so I finally looked them up:

  • league: the distance a man walks in an hour (about three miles, unless you are Aragorn son of Arathorn)
  • fathom: about six feet, literally “a pair of outstretched arms” (for a full-grown man, presumably)
  • furlong: a eighth of a mile, but originally used to describe the length of a furrow, which was the long side of a then-standard rectangular acre-plot (the short side was 22 yards or “one chain” wide). Thank you, Wikipedia!

  • I already knew that “fortnight” was “two weeks” but somehow hadn’t connected it as “fortnight” = “fourteen nights”. Wikipedia’s entry on the FFF System makes for some fun related reading.

    I remain stymied by some other words Tolkien uses, though; most are landscape words. I cannot find any reasonable definitions for “hythe” (a place where a boat comes ashore, from context?), “mew” (something on a hill), or “thrawn” (a kind of tree, from context). If you have any hints, please share in the comments. Thanks!