incubus (n.)youdaoicibaDictYouDict[incubus 词源字典]
c. 1200, from Late Latin (Augustine), from Latin incubo "nightmare, one who lies down on (the sleeper)," from incubare "to lie upon" (see incubate). Plural is incubi. In the Middle Ages their existence was recognized by law.[incubus etymology, incubus origin, 英语词源]