Hippopotomonstrosesquipedaliophobia also known as Sesquippedalophobia
What is it?
It is fear of long words. No I am not joking. You can google it and you will find it.
Wikipedia has listed Hippopotomonstrosesquipedaliophobia as a jocular or fictional phobia.
The fear of long words however is a real fear. I have come across a few case studies where people appear to have intense physical reactions when they are faced with reading, writing or saying long words. A few of those people said the fear stemmed from childhood where they suffered from a learning difficulty or speech impediment that made long words harder to cope with than small ones.