Wikipedia
Echthroi (Ἐχθροί) is a Greek plural meaning "The Enemy" (literally "enemies"). The singular form of the word, Echthros (Ἐχθρός), is used in many versions and translations of the Bible for "enemy".
Historically used primarily in connection with biblical and classical subjects, the term has more recently been used to refer to a fictitious type of evil being, principally in Madeleine L'Engle's " Time Quartet". A personification of the forces of impersonalization and nihilism, they exist in both the macrocosmic and microcosmic level, counteracted principally by what L'Engle refers to as "Naming", or re-integration of a character with its best-motivated identity ('true self'). These concepts appear in one form or another in a number of L'Engle's books, as part of her recurring themes of good versus evil, interdependency, and the role of the individual in the cosmic scheme of things.