Other forms: namelessly
Someone or something that has no name is nameless. You can also describe someone as nameless when you choose not to identify them or reveal their name publicly.
A nameless source for a newspaper article is anonymous — in other words, they have a name but it's being kept private. When you're talking about someone whose identity you won't reveal, you can refer to them as "someone who shall remain nameless." A nameless fear, on the other hand, is one that's so scary it can't be captured in words or given a name.