Plurali, and why that is definitely wrong.

So what did I learn today? This:

Graffiti is plural.
Who knew?
I didn't.
One piece is a graffito.
Graffito comes from the Italian meaning "little scratch" or "scribble". It doesn't quite translate that way anymore, but it did.

The same is true of spaghetti. A single strand is a spaghetto. My mum told me that. I'm sure there are other examples of Italian words tricking me with their rare -o singular and common -i plural, but I can't think of any.

Here's another thing about plurals.

So in English, our standard way of making plurals is by adding an "s", or at least a variation that ends in "s".

Word becomes words.
Baby becomes babies.
Box becomes boxes.

However, I'm sure you were already aware, being skilled users of the English language, that we have some plurals that don't end in "s".

Woman becomes women.
Foot becomes feet.
Mouse becomes mice.

There are many examples.

Some people use octopi as the plural for octopus, but this is incorrect. Octopuses is correct. The -i ending tends to be Latin words, fungus becoming fungi, for example. But octopus is a Greek word, not Latin, so it has never been correct to say octopi.

My favourite plural (yes, I have a favourite plural) is: passersby.

It's the only word I can think of (and feel free to shatter my dreams by finding other examples) where an "s" is used to indicate plural, but that "s" isn't found at the end of the word.
I am aware of hyphenated examples such as "days-off" or "sisters-in-law", but I can't think of a single word like passerby which is changed in this way.