Any irrational fear - and it MUST be irrational - is a phobia and will have a long word ending in ~phobia as its medical term. A fear of snakes is not a phobia, it's perfectly proper to be afraid of...
the word that means "fear of words" is wordphobia
hippopotomonstrosesquipedaliophobia hippopotomonstrosesquippedaliophobia is a common, but incorrect, misspelling.
hippopotomonstrosesquipedaliophobia