Quote Originally Posted by GoktimusPrime View Post
Octopodes is also another accepted English plural for "octopus"! As far as Latin is concerned, "octopodes" is used as the plural for octopus in the nominative, accusative and vocative plural, but "octopi" is the plural in the second and third declension. Octopi is more widely used in English because while the word is Greek in origin, it came to English via Latin.
If it were a Latin word, octopus would be a third declension noun, and the plural is octopodes, based on the Greek ὀκτώποδες. It's not a second declension noun. In English, octopuses is the most correct plural. Octopi only exists as a result of mistaken construction, like saying the plural of virus is viri.