Octopuses are completely deaf.
Sound reasons for silence: why do molluscs not communicate acoustically?
To pluralize Octopus we must use the origin of the word:
- octopuses is the most common form in the UK as well as the US;
- octopodes is rare,
- and octopi is often objectionable.
The Oxford English Dictionary lists octopuses, octopi and octopodes (in that order);
it labels octopodes “rare”, and notes that octopi derives from the mistaken assumption that octōpūs is a second declension Latin noun, which it is not. Rather, it is (Latinized) Ancient Greek, from oktṓpous (ὀκτώπους), gender masculine, whose plural is oktṓpodes (ὀκτώποδες).
If the word were native to Latin, it would be octōpēs (‘eight-foot’) and the plural octōpedes, analogous to centipedes and mīllipedes, as the plural form of pēs (‘foot’) is pedes.
In modern Greek, it is called khtapódi (χταπόδι), gender neuter, with plural form khtapódia (χταπόδια).