The plural octopi is hypercorrect, coming from the mistaken notion that the -us in octopūs is a Latin second declension ending. The word is actually treated as a third declension noun in Latin. The plural octopodes follows the Ancient Greek plural, ὀκτώποδες (oktṓpodes).
Thursday, 16 February 2017
TIL: The Real Plural of "Octopus"
Today I learnt that "octopi" is actually technically incorrect as the plural form of "octopus". Following its Greek roots, the correct plural form would be "octopodes". To quote Wiktionary:
The same applies to "platypus": the plural of "platypus" is either "platypuses" or "platypodes".
However, standard English dictates that the plurals of "octopus" and "platypus" are "octopuses" and "platypuses" respectively.