octopii

In imitation of Latin nominative plural forms of nouns ending in ius. Compare walrii and penii.

octopii

1. (nonstandard, proscribed, rare) Misconstructed plural form of octopus.

• The plural form *octopii is doubly incorrect. Firstly, octopus derives from Greek, not Latin; its etymologically-consistent plural form is octopodes. Secondly, even if octopus were a second-declension Latin noun, the plural form would be *octopi; in the correct plurals radii and gladii, with which *octopii is analogous, the first ‘i’s are part of the words’ stems (radi- and gladi-), and not their case endings — for *octopii to be the plural, *octopius would need to be the singular.