What is the root word of grotesque?

The root word of "grotesque" is "grotesque" itself. It comes directly from the Italian word "grottesco" which means "of a cave" or "cavernous."

The word originated from the discovery of ancient Roman and Greek decorations in the 15th century, found in caves and grottos. These decorations often featured fantastical and exaggerated figures, which gave rise to the term "grotesque" to describe such artistic styles.

So, while the word itself isn't derived from a simpler root, it's directly linked to the origin of the concept it represents.