sesquipedalianism

noun2

1. •
   The practice of using long, sometimes obscure, words in speech or writing.

   • His voice here is a marvelous juxtaposition of cool elegance, unaffected hipness, unabashed sesquipedalianism ("the rich bouquet of exuded sebaceousness") and swell conversational slang (...) — 1995
2. •
   A very long word.