Perhaps it is not current usage, but I guess it might have be common English usage till 19th century. I think that I have seen corn used generically in novels a

Perhaps it is not current usage, but I guess it might have be common English usage till 19th century. I think that I have seen corn used generically in novels and other works from before that time. May be you can find reference to corn in Chaucer, I don't exactly remember if it is there for sure.