What is the root and meaning of synonym?

The root of the word "synonym" is Greek. It comes from the combination of two words:

* syn-: meaning "together" or "with"

* onoma: meaning "name"

Therefore, "synonym" literally means "same name".

This reflects the meaning of the word: synonyms are words that have the same or nearly the same meaning. For example, "happy" and "joyful" are synonyms.