That gets down to what you mean by “acceptable”. Octopi is not a natural derivation of octopus as the plural is octopodes just like “aint” is not a natural derivation of any form of the verb “is” BUT in both aint and octopi’s case most understand those words so they might be acceptable depending.
That gets down to what you mean by “acceptable”. Octopi is not a natural derivation of octopus as the plural is octopodes just like “aint” is not a natural derivation of any form of the verb “is” BUT in both aint and octopi’s case most understand those words so they might be acceptable depending.