goose vs greylag

goose and greylag both are nouns.

Word	Noun	Adjective	Verb	Adverb
goose	Yes	No	Yes	No
greylag	Yes	No	No	No

As nouns, greylag is a hyponym of goose; that is, greylag is a word with a more specific, narrower meaning than goose:

goose: web-footed long-necked typically gregarious migratory aquatic birds usually larger and less aquatic than ducks
greylag: common grey wild goose of Europe; ancestor of many domestic breeds

goose (noun)	greylag (noun)
web-footed long-necked typically gregarious migratory aquatic birds usually larger and less aquatic than ducks	common grey wild goose of Europe; ancestor of many domestic breeds
flesh of a goose (domestic or wild)
a man who is a stupid incompetent fool