What does W.O.N. mean?

I just downloaded a hair snood pattern from 1944 and the first row reads K. 2tog., W.O.N. (thus making a st.) can anyone explain this abbreviation. Thank you:knitting:

According to Vintage Purls ( http://www.vintagepurls.net.nz/abbreviations.html ) , it is used to make a st in between a purl and a knit st…so after you are done your purl, you would bring the yarn over the needle to the back, ready for the next knit st.

HTH
Katy

Wool Over Needle—a YO