1.
unknown, obscure, nameless
Not famous or well-known. Used to describe people, places, or things that have not gained recognition or fame.
2.
anonymous
Having no name attached, or the identity is not known or disclosed.
Common patterns
Used as a noun (無名) and as a no-adjective modifier (無名の).
Similar words
無名 (unknown/nameless) is the opposite of 有名 (famous). The pair 無名/有名 shares the same structure: 無/有 (without/with) + 名 (name/fame).
Special usage
In the context of Japanese swords, 無名 (also read むめい) specifically means the blade lacks the swordsmith's inscription (銘) on the tang.