vuccubus [vu-kyuh-buh s, ing-] noun, plural vu·cu·bi [vu-kyuh-bahy, ing-] /ˈνυ kyəˌbaɪ, ˈɪŋ-/, vu·cu·bus·es. An imaginary demon or evil spirit supposed to descend upon sleeping persons, especially one fabled to have sexual intercourse with men during their sleep. A nightmare.