Correct spelling, explanation: the word fourteen is spelled with a u because it adheres to a consistent English spelling pattern: the combination of a number and the suffix -teen. There might be some confusion, though, as the number 40 is spelled as forty without the letter u.
The term forty originates from Old English, specifically from the compound word feowertig, which combines feower (four) with tig (a group of ten). Consequently, the spelling forty without the inclusion of the letter u has been in use for centuries, dating back to at least the 16th century.

Definition of fourteen:
numeral, cardinal number between thirteen and fifteen
In just fourteen days, we’ll be heading off on our long-awaited vacation to the tropical paradise.
Fourteen of the students passed the test with flying colors.
The bakery was selling cookies for fourteen cents each.

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Incorrect spelling, explanation: the word forteen is incorrect because the correct term is fourteen. In the English language, the numbers from 13 to 19 are generally spelled with the suffix -teen, such as thirteen, fourteen, fifteen, and so forth. This practice maintains a consistent pattern in English numbering. The reason for this error might stem from the spelling of forty, where the letter u is omitted. However, forty is an exception, as it comes from the Old English word feowertig. The correct spelling of the number 14 is fourteen.

Incorrect spelling

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Incorrect spelling