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]