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An epithet (from Greek: ἐπίθετον epitheton, neuter of ἐπίθετος epithetos, "attributed, added") is a byname, or a descriptive term (word or phrase), accompanying or occurring in place of a name and having entered common usage. It can be described as a glorified nickname. It has various shades of meaning when applied to seemingly real or fictitious people, divinities, objects, and binomial nomenclature. It can also be a descriptive title: for example, Alfred the Great, Suleiman the Magnificent or Władysław I the Elbow-high.

In contemporary use, epithet often refers to an abusive, defamatory, or derogatory phrase, such as a racial or animal epithet. This use as a euphemism is criticized by Martin Manser and other prescriptive linguists.

In linguistics, an epithet only can be a metaphor, essentially a reduced or condensed use of apposition. Epithets are sometimes attached to a person's name or appear in place of his or her name, as what might be described as a glorified nickname or sobriquet. An epithet is linked to its noun by long-established usage. Not every adjective is an epithet. An epithet is especially recognizable when its function is largely decorative, such as if "cloud-gathering Zeus" is employed other than in reference to conjuring up a storm. "The epithets are decorative insofar as they are neither essential to the immediate context nor modelled especially for it. Among other things, they are extremely helpful to fill out a half-verse", Walter Burkert has noted.

Some epithets are known by the Latin term epitheton necessarium because they are required to distinguish the bearers, e.g. as an alternative to numbers after a prince's name—such as Richard the Lionheart (Richard I of England), or Charles the Fat alongside Charles the Bald. The same epithet can be used repeatedly joined to different names, e.g. Alexandra the Great as well as Marianette the Great and Regiana the Great.

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