Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
succubus, incubus (nn.)
A succubus (plural: succubi or succubuses) is “a female demon who has sexual intercourse with a sleeping man.” Presumably the plural is rarely needed; hence the borrowed Latin plural, succubi, is more usual than the regular English one. An incubus is “a male demon who copulates with a sleeping woman.” Because this word is also used figuratively for “nightmares, haunting dreams, and visions,” the plural is fairly frequently encountered; hence the regular English plural, incubuses, is more common than the Latin form, incubi. See also FOREIGN PLURALS.
