A male spirit or demon that visits a sleeping woman for purposes of having sexual intercourse with her; a female demon who likewise visits a sleeping man. This is a particularly vivid manifestation of two very basic and common ideas in human history: The first is that sexual intercourse can take place between mortals and gods or supernatural beings; the second is that nightmares are the result of an external will, such as that of a lewd demon. The word INCUBUS comes from the late Latin incubus and incubo, meaning “nightmare.” These derive from the classical Latin incubare, meaning to lie upon (with succubare meaning “to lie under”). The second entry under “incubus” in the Oxford English Dictionary defines it as “a feeling of oppression during sleep, as of some heavy weight on the chest and stomach; the nightmare.”
The incubus may remain invisible to the woman he is visiting, but if he appears to her, he normally does so in the form of her lover. Despite the familiar form, the woman finds the sex unpleasant, although the erotic element makes it an ambiguous experience. Often the incubus has been thought to subject the woman to sexual depravity, lust, and terrifying nightmares. Incubi were generally deemed sterile, but they were able to impregnate women with semen collected from nocturnal emissions of men. Reports of incubi visitations were always more common among women than men and among virgins and widows than among married women; they were most prevalent among nuns.