From The Collaborative International Dictionary of English v.0.48 :
Graylag \Gray"lag`\, n. (Zool.) The common wild gray goose ({Anser anser) of Europe, believed to be the wild form of the domestic goose. See Illust. of Goose. [1913 Webster]From WordNet (r) 3.0 (2006) :
graylag n 1: common grey wild goose of Europe; ancestor of many domestic breeds [syn: greylag, graylag, greylag goose, graylag goose, Anser anser]