incubus

An evil spirit supposed to descend upon and have sexual intercourse with women as they sleep.

A nightmare.

An oppressive or nightmarish burden.

The nightmare.

An imaginary being or demon, supposed to be the cause of nightmare; especially, such a being of the male sex who was supposed to consort with women in their sleep.

Figuratively, a heavy or oppressive burden; especially, a heavy weight on the mind; anything that prevents the free use of the faculties.

[capitalized] In entomology, a genus of parasitic hymenopters of the family Braconidæ: synonymous with Microgaster of Latreille.

A demon; a fiend; a lascivious spirit, supposed to have sexual intercourse with women by night.

The nightmare. See Nightmare.

Any oppressive encumbrance or burden; anything that prevents the free use of the faculties.