What is the root of word ungrammatical?

The root of the word "ungrammatical" is gramma. This comes from the Greek word gramma, meaning "letter" or "writing."

Here's how it breaks down:

* gramma (Greek) -> grammar (English)

* un- (prefix meaning "not") + grammatical -> ungrammatical

Therefore, "ungrammatical" literally means "not according to the rules of grammar."