sesquipedalophobia

Meaning: Fear of long words

Root from Latin sēsquipedālis (literally “a foot and a half long”), from Latin sēsqui (“one and a half times”) + Latin pedālis (“measuring a foot, foot (relational)”)

And to make it even longer, non-nonsensical parts were added to make: 

hippopotomonstrosesquipedaliophobia

sources: 

• https://en.wiktionary.org/wiki/sesquipedalophobia#English
• https://en.wiktionary.org/wiki/sesquipedalian#English 
• https://en.wiktionary.org/wiki/hippopotomonstrosesquipedaliophobia