Anonymous

(a.) Nameless; of unknown authorship; as, an anonymous benefactor; an anonymous letter.

Thesaurus Entries

closet, cryptonymic, cryptonymous, incognito, inmost, innermost, innominate, interior, intimate, inward, isolated, nameless, personal, private, privy, retired, secluded, sequestered, unacknowledged, undefined, undesignated, unidentified, unknown, unnamed, unrecognized, unspecified, withdrawn, without a name