Magniloquence is a noun that refers to use of high-flown language.

In Latin, the word Magnus (MAG nus)  means ‘great,’ while the word loqui (LOW kwi) — also from Latin — means ‘speak.’ It’s responsible for words like eloquence. To speak in a ‘great’ or over-the-top manner is to speak with magniloquence.

Mr. Sanderson’s magniloquence made him seem bright and well-accomplished, but behind all those high-flown words, he was really just a narcissist who liked to use big words.