anonymous

If you don't know who wrote a poem, the author is anonymous. If you don't know who donated a gift to a museum, it's called an anonymous gift from an anonymous donor. Anonymous means a person unknown.

Alcoholics Anonymous takes its name from the fact that it's a confidential group––people use only their first names and do not identify one another as members of the group. Another related meaning of anonymous is to describe something that does not have any special qualities. If you work in an anonymous office building, its design is pretty typical and not very interesting.

Definitions of anonymous
1

adj having no known name or identity or known source

anonymous authors”
anonymous donors”
“an anonymous gift”
Synonyms:
anon.
nameless, unidentified, unknown, unnamed
being or having an unknown or unnamed source
Antonyms:
onymous
bearing a name
binomial, binominal
having or characterized by two names, especially those of genus and species in taxonomies
pseudonymous
bearing or identified by an assumed (often pen) name
show more antonyms...

adj not known or lacking marked individuality

“brown anonymous houses”
anonymous bureaucrats in the Civil Service”
Synonyms:
faceless
without a face or identity