Epithet

An epithet is an adjective or adjectival phrase defining a characteristic or ascribes of a thing or person [Baldick, p. 86].
An epithet is a word or phrase characterizing a noun and is related to it (in grammar and stylistics). For example, The Bard (William Shakespeare), The King (Elvis Presley), Richard the Lionheart (Richard I, King of England), etc. [Crystal, p. 171].
A word or phrase that operates as part of someone’s name or describes a noun is called an epithet [Quinn, p. 145].
An epithet is an adjective or phrase expressing a characteristic of a person or thing. In literature, the term is defined as an element of poetic diction that differentiates the language of verse from the everyday language [Britannica Online Encyclopedia].
An epithet is a descriptive term identifying an attribute. It is a valid literary or rhetorical device for describing a character to the reader.
There are three main epithets [YourDictionary]:
 Fixed epithets (the author repeats epithets over several scenes).
 Kennings (a compound or two-word metaphorical expression that replaces a noun).
 Derogatory epithets (teasing nicknames to ethnic, racial, or homophobic slurs; are meant to insult an opponent or group of people without directly stating the targeted characteristic).

Sources:

⠀ Chris Baldick. (2015). The Oxford Dictionary of Literary Terms. Oxford: Oxford University Press.

⠀ David Crystal. (2008). A Dictionary of Linguistics and Phonetics, 6th Edition. New-Jersey: Wiley-Blackwell.

⠀ Epithet. Britannica Online Encyclopedia. Retrieved from: [https://www.britannica.com/art/epithet].