What word in the English language is always spelled incorrectly?

Incorrectly, as that is the proper spelling of the word

Misspelled is the word in the English language that is always spelled incorrectly.

There are English words that may sometimes be spelt incorrectly based on its pronunciation. But, whenever we see the incorrectly spelled word, we always say that the word is misspelled.

Misspell is a combination of two words. Mis and spell. Mis is a prefix applied to various parts of speech, meaning ill or wrong or incorrect or simply negating.

Spell is a verb used with object which means to name, write, or give the letter in order.

With these definitions, misspell is the incorrect or wrong writing of the name or order of letters in a word.