anonym

n. one who is anonymous; assumed or false name, pseudonym

Anonymity is derived from the Greek word ανωνυμία, meaning "without a name" or "namelessness". In colloquial use, the term typically refers to a person, and often means that the personal identity, or personally identifiable information of that person is not known. More strictly, and in reference to an arbitrary element (e.g. a human, an object, a computer), within a well-defined set (called the "anonymity set"), "anonymity" of that element refers to the property of that element of not being identifiable within this set. If it is not identifiable, then the element is said to be "anonymous".
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Noun
1. a fictitious name used when the person performs a particular social role
(synonym) pseudonym, nom de guerre
(hypernym) name
(hyponym) stage name

adv. anonymously, namelessly, without a name

adj. anonymous, nameless, of an unknown person, faceless, unknown, lacking identity; dark, dim, mysterious, not clear

(n.)
One who is anonymous; also sometimes used for "pseudonym."
  

(n.)
A notion which has no name, or which can not be expressed by a single English word.