Anonymous (adjective)

1. Having no known name or identity.
2. Not named or identified.

Origin:

From the greek word "anōnymos" meaning "having no name".

Examples:

1. The letter was written by an anonymous person.
2. The donation was made by an anonymous benefactor.
3. The author's name was anonymous on the manuscript.
4. He chose to remain anonymous in the newspaper article.
5. The call was made by an anonymous caller.