/in"kyeuh beuhs, ing"-/ , n. , pl. incubi /-buy'/ , incubuses .
1. an imaginary demon or evil spirit supposed to descend upon sleeping persons, esp. one fabled to have sexual intercourse with women during their sleep. Cf. succubus (def. 1).
2. a nightmare.
3. something that weighs upon or oppresses one like a nightmare.
[ 1175-1225; ME incubare to lie upon; see INCUBATE ]