All those vowels at once are enough to get any new Italian speaker into trouble – and that's apt, because il guaio means difficulty, a snag, a predicament, a pickle.
Il guaio è che è già tardi.
The trouble is that it's already late.
Siamo in un bel guaio!
A fine mess we're in!
One way to remember it is to think of it as the English word 'woe': the two are believed to come from the same root, the old Germanic term 'wai', an exclamation of pain or suffering.
Today you'll often see it in its plural form, guai.
È in un sacco di guai.
She's in a lot of trouble.
Sometimes you seek trouble out, especially if you're una fonte di guai (a troublemaker)...
Il va sempre a caccia di guai.
He's always looking for trouble.
... and sometimes it just finds you.
Sono finito nei guai con i vicini.
I ended up in trouble with the neighbours.
You can also use the term as a warning to others – the same way you can say 'woe betide...' in English.
Guai a chi la tocca!
Woe betide anyone who touches her!
(That one's a line from the Puccini opera Manon Lescaut)
Guai a te se lo fai un'altra volta!
If you do that again you'll be sorry!
Simplest of all, you can just exclaim "Guai!" in the direction of someone misbehaving to let them know they'd better watch themselves.
Do you have a favourite Italian word you'd like us to feature? If so, please email our editor Jessica Phelan with your suggestion.