• 4-minute read
• 19th August 2019

Octopuses or Octopi? (Tricky Latin and Greek Plurals)

Being around more than one octopus can be stressful. And this isn’t just because our cephalopod friends are shapeshifting, super-powered geniuses. It’s also because, like many words with Latin or Greek origins, ‘octopus’ has more than one plural in English. And not knowing whether to call them ‘octopuses’ or ‘octopi’ is a recipe for social awkwardness.

But is one correct? Or is it a matter of preference? And has anyone asked an octopus? Let’s look at some tricky Latin and Greek plurals to find out.

Latin and Greek Plurals

Many English words come from Latin or Greek. As a result, some still follow Latin or Greek spelling rules when forming a plural. For instance, ‘abacus’ comes from Latin. And since ‘-us’ word endings in Latin change to ‘-i’ in the plural, the English plural can be spelled ‘abaci’.

However, most English plurals are formed by adding ‘-s’ or ‘-es’. And modern English frequently has conventional plurals for Latin and Greek terms. The plural of ‘abacus’, for instance, can also be spelled ‘abacuses’.

In other words, the plural forms of Latin and Greek words can often be either regular (i.e. ending in ‘-s’ or ‘-es’) or irregular (i.e. spelled with a different word ending). And while we’ve looked at some of the rules about irregular plurals previously, here we’re going to examine some tricky Latin and Greek plurals in more detail, starting with our tentacled friends…

1. Octopuses, Octopi and Octopodes

Since ‘octopus’ ends in a ‘-us’, most people assume it comes from Latin and spell the plural ‘octopi’. But this is a false etymology: ‘octopus’ comes from Greek, so the correct plural would be ‘octopodes’.

Luckily, English is a fairly free and easy language these days, so both ‘octopi’ and ‘octopodes’ are acceptable spellings. To avoid the Latin/Greek controversy, though, you could just use ‘octopuses’ instead!

2. Ignorami?

‘Ignoramus’ is an interesting word because it does come from Latin, but the plural does not. The root of this word is ignōrāmus, which meant ‘we do not know’. It was never a noun in Latin, though, so we cannot pluralise it as ‘ignorami’. It should always be ‘ignoramuses’.

3. Criteria or Criterion?

In this case, it’s not that ‘criteria’ is incorrect or old-fashioned. Rather, problems arise because the singular ‘criterion’ is rare enough that people assume ‘criteria’ is singular!

This is not the case, though: ‘criteria’ is always plural (with ‘criterions’ a rare plural variant). The singular term here is ‘criterion’. This contrasts with ‘data’, which was originally a plural but is now often used as a singular term (instead of ‘datum’, the original Latin noun).

4. Academia vs. Everyday Life

Finally, we have words where the correct plural depends on the situation. In science and maths, for example, Latin plurals such as ‘foci’ and ‘formulae’ are fairly common. But in everyday life, we are far more likely to use ‘focuses’ and ‘formulas’. So the best term may depend on the situation.

It is generally the more scientific fields that use the Latin and Greek plural endings, but this isn’t always true. For instance, a surgeon is more likely to use the Anglicised ‘appendixes’ when referring to the internal organ, while a publisher will use the Latin ‘appendices’ for pages at the end of a book.

The key here, then, is to consider the context. If you’re not sure which word to use, check online to see if one term is more common. If not, pick one spelling and use it consistently. And don’t forget that having your work proofread is a great way to root out errors and inconsistencies.