The word you are interested in, “hippopotomonstrosesquippedaliophobia,” could be considered a “real word” since it enjoys some currency as a term for fear of long words, but like many other oddball or super-long words, it is a fabricated novelty item whose use is mostly confined to people in the act of pointing it out. In other words, I doubt you will find it used in ordinary conversation much if at all, or in textual uses where the point is not, again, to point out the word.

Its fanciful nature is evident in its first part, “hippopotomonstro-.” Breaking down its components, we see something like “river horse [see the origin of “hippopotamous” in Merriam-Webster’s Collegiate Dictionary, Tenth Edition] monster.” There is no connection there that I can see to words at all. We do enter an adjective “sesquipedalian” in the Collegiate which is worth consulting.

As might be obvious at this point, the reason you won’t find “hippopotomonstrosesquippedaliophobia” entered in our dictionaries at this point is because of its extreme rarity. Regardless of how fanciful a concoction it is, if it ever satisfied our general criteria of frequency and establishment in mainstream English usage it would become a candidate for inclusion. We will keep our eyes out for this monstrosity, though we are already aware of it and many other contrived “-phobia” terms.

Thank you for writing.

Sincerely,

Thomas Pitoniak, Ph.D.

Associate Editor

Merriam-Webster, Inc.