Synonymous (adjective)

1. Meaning the same or very similar to another word or expression.
2. Meaning the same as another word or phrase.
3. Used to describe words that have the same or almost the same meaning.

Origin:

From the greek word "synonymos" meaning having the same name, from "syn" meaning together and "onoma" meaning name.

Examples:

1. Happy and Joyful are synonymous.
2. The words "big" and "large" are synonymous.
3. The word "synonymous" is synonymous with "similar" in meaning.
4. The words "car" and "automobile" are synonymous.
5. The words "sad" and "depressed" are synonymous.