“Zig-zag” is first attested in English as a garden path layout in 1712. Its earliest appearance is in German (zickzack), indicating a proper path toward a siege so that the defenders don’t have a clear shot at the besiegers. In The Hobbit, the term describes the path into well-hidden and well-fortified Rivendell.
- 03.012 in the dusk down the steep zig-zag path
OED reports that it can be two words, one word, or hyphenated.
“zigzag, n., adj., and adv.”. OED Online. Oxford University Press, March 2015. Web. 9 May 2015.