Hippopotomonstrosesquipedaliophobia: fear of long words. 🙂
From hippopotomonstrosesquipedalian, an extension of sesquipedalian with monstrum (monster) and a misspelled form of hippopotamus. The hippo and monstro part were added to exaggerate the length of the word itself.
The Latin word sesquipedalis means “a foot and a half long”. The poet Horace used the word in his Ars Poetica in reference to writers who use very long words, or, in Latin, sesquipedalia verba.