Demons (male and female, respectively) who seek to have sexual intercourse with sleeping humans. In medieval Europe some believed that union with an incubus resulted in the birth of witches, demons, and deformed human offspring. Merlin was said to have been fathered by an incubus
() From Late Latin incubus Latin incubo (“nightmare, one who lies down on the sleeper”) incubāre (“to lie upon, to hatch”) in- (“on”) + cubāre (“to lie”).