Same word root as Bison? wow.
And the egg-sucking derivation is classy, too.
O.E. weosule, wesle “weasel,” from P.Gmc. *wisulon (cf. O.N. visla, M.Du. wesel, Du. wezel, O.H.G. wisula, Ger. Wiesel), probably related to P.Gmc. *wisand- “bison” (see bison), with a base sense of “stinking animal,” because both animals have a foul, musky smell (cf. L. vissio “stench”). The verb “to deprive (a word or phrase) of its meaning” is first attested 1900, so used because the weasel sucks out the contents of eggs, leaving the shell intact; the sense of “extricate oneself (from a difficult place) like a weasel” is first recorded 1925; that of “to evade and equivocate” is from 1956. A John Wesilheued (“John Weaselhead”) turns up on the Lincolnshire Assize Rolls for 1384, but the name seems not to have endured, for some reason.
Online Etymology Dictionary, © 2001 Douglas Harper