A mononym is a name composed of only one word. An individual who is known and addressed by a mononym is a mononymous person.
A mononym may be the person's only name, assigned to them at birth. This was routine in most ancient societies, and remains common in modern societies such as in Afghanistan, Bhutan, Indonesia, Java, Myanmar, Mongolia, Tibet, and South India.
In other cases, a person may select a single name from their polynym or adopt a mononym as a chosen name, pen name, stage name, or regnal name. A popular nickname may effectively become a mononym, in some cases adopted legally. For some historical figures, a mononym is the only name that is still known today.
The word mononym comes from English mono- ("one", "single") and -onym ("name", "word"), ultimately from Greek mónos (μόνος, "single"), and ónoma (ὄνομα, "name").
The structure of persons' names has varied across time and geography. In some societies, individuals have been mononymous, receiving only a single name. Alulim, first king of Sumer, is one of the earliest names known; Narmer, an ancient Egyptian pharaoh, is another. In addition, Biblical names like Adam, Eve, Moses, or Abraham, were typically mononymous, as were names in the surrounding cultures of the Fertile Crescent.
Ancient Greek names like Heracles, Homer, Socrates, and Aristotle, also follow the pattern, with epithets (similar to second names) only used subsequently by historians to distinguish between individuals with the same name, as in the case of Zeno the Stoic and Zeno of Elea; likewise, patronymics or other biographic details (such as city of origin, or another place name or occupation the individual was associated with) were used to specify whom one was talking about, but these details were not considered part of the name.
A departure from this custom occurred, for example, among the Romans, who by the Republican period and throughout the Imperial period used multiple names: a male citizen's name comprised three parts (this was mostly typical of the upper class, while others would usually have only two names): praenomen (given name), nomen (clan name) and cognomen (family line within the clan) — the nomen and cognomen were almost always hereditary.