I'm not sure how much French you know, but the dictionary at http://www.cnrtl.fr/definition/
almost always has some etymological information and you can look just at the etymological information by going to http://www.cnrtl.fr/etymologie/
As for yeux, it might be surprising, but like http://www.cnrtl.fr/etymologie/oeil
says, the word derives regularly from Latin, with oeil < oculum and yeux < oculos. I don't know all the details -- it involves palatalization which had complicated effects -- but I can see that the development of the end of the word is regular -- it's similar to words like cheval < caballum, plural chevaux < caballos. But to get at the details, you need to also know the Old French forms.