Stoats (Mustela erminea) are in the same family as weasels, wolverines, mink, badgers and otters. When in their winter white form they are called ermine. Their class is Carnivora (They are just cute enough to look like a rodent which they eat.) http://www.fact-index.com/s/st/stoat.html
sorry, clarification: the less fancy name for Mustela is in fact weasel. The Family weasel includes the Subfamilies weasel and a bunch of others. So it could be called a weasel but is not what is generally concidered a weasel. (Have I made this clear as mud yet?)