A clew is a ball of thread, but the word has branched out (as words do) and now it also means the lower corners of a sail (or, if it's a triangular sail, the back bottom corner).
Clew lines are ropes attached to the clews as a means of furling the sail. From here clew has also come to mean the rigging of a hammock.
I must agree that hammocks and sailing ships are hard things to spot, but, hey, they're nice to dream about, aren't they, as we face the doleful battle that is so often Monday morning.
The ball-of-thread sort of clew is quite easy, though: and if you haven't got one of those you can always can clew something yourself, because as a verb clew means to roll into a ball.
The thing I like most about the word clew, though, is that it's basically the same word clue. Isn't that great? You unravel a mystery just in the same way as you might unravel a ball of string.
I suppose this means that clew/clue is yet another contranym, doesn't it, because it means to roll up as well as to tease out.
And you know, there seem to be so many of contranyms about that sometimes it seems a wonder that any of us have a clue what we're going on about.
Spot the frippet: clew. This word comes from the Old English cliewen, and is related to the Old High German kliu, which means ball.