Mike, 2nd wave feminism could actually have been considered WGTOW, very much so. Things have gotten a little distorted in the modern feminism variant. Feminists these days don't particularly care for PUAs or woman-blaming, which is kind of what both offshoots of MRA do. I'm not saying that some groups of feminists don't do their share of man-blaming, but this really isn't representative of feminism on the whole. I personally am a feminist, a fairly passionate one, and I think MGTOW is great (though there are some pretty angry men in it, thats for sure). If there were a definition for WGTOW, I would be one. I don't feel I need a movement though, because there are already so many women are foregoing marriage and the traditional compliances expected by society, thank you feminism, that another movement to do essentially the same thing that feminism sought to do (though whether feminism actually "achieved" that goal is most definitely questionable).
Also, Elena's answer below is entirely biased and bordering on fallacy.