> I looked up fé and dýr in Gordon's glossary, but promptly forgot their
> genders and was too lazy to look them up again so just guesstimated that
> they might both be neuter as the same words are in German (Vieh, Tier). Is
> that a reasonable approach when the words are so obviously related?

Yes, I suppose it is. My guess is that you'll be correct about 8 or 9 times
out of 10. The guesstimate works on both the words you mention.