Why "anual" isn't in the dictionary: the importance of double "n"

What kind of error is it?

Spelling error

Why do people make this mistake?

The error often occurs because "anual" appears similar to the correct word in English but omits the necessary double "n". The pronunciation of "annual" doesn't strongly emphasize the second "n", leading to misspellings based on how the word sounds rather than how it is spelled.

What is correct?

The correct spelling of the word is "annual". It is an adjective that describes something that occurs once every year or is related to a year.