There are those who think that Grey Lag Geese get their name from their habit of being the last to migrate in Winter, in other words they lag behind. This makes no sense to this poor fool as other European languages simply call this bird 'grey goose' (Grauwe Gans, Graugans, Grågås, Oie Cendrée and so on). So a little bit of detective work pulled out another derivation that says that 'lag' is an ancient word for goose, a 13th century text refers to 'redlag' which is supposed to translate as 'reed goose', and the lag part reflecting in some way the noise made by these birds. Scientists with no sense of romance simply call them Anser anser or goosey goose if you like.
Weekend Reflections are here.