Correct spelling, explanation: eighteen is the word for the number 18, and it’s a conjunction of the words eight and teen. This is quite logical, the only issue is – should the t be doubled, or not? Considering the fact that the first one ends in t and the second starts with it, it could be reasonable. But the language always strives to be as simple as possible – and in this case, the pronunciation does not suggest that the tt is needed here. So, because of that, always keep in mind that eighteen only needs one t in the middle.

Definition of eighteen:
noun
1. the number 18
In Europe, you can buy alcohol when you’re eighteen, but in the US you have to be over twenty-one.
Over the eighteen months, I have changed my career, got in shape, and found a girlfriend – it’s been a good year and a half!

Incorrect spelling, explanation: eightteen may seem like a logical choice, given that the word consists of eight and teen. But you may notice that it looks a bit unnatural. This is because we know we don’t pronounce the double t. We only pronounce one, as it’s the most convenient way to speak. And because the language is shaped to be as convenient as possible, eighteen is the correct spelling here.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling