Of a book, letter, etc.: of undeclared authorship or source, anonymous. Obsolete.

figurative. Of a book, statement, etc.: without a known author; anonymous. Now rare.

Of unknown or undeclared authorship; not bearing the name of the author; anonymous.

Of a writer or writing: anonymous.

(un-, prefix1 affix 2.)

Of unknown authorship or provenance. Now rare.

(un-, prefix1 affix 1b).