incubus

Meanings

1. An evil spirit supposed to oppress people while asleep, especially to have sex with women as they sleep.
2. A feeling of oppression during sleep, sleep paralysis; night terrors, a nightmare.
3. Any oppressive thing or person; a burden.
4. One of various of parasitic insects, especially subfamily Aphidiinae.

Etymology

From Late Latin incubus, from Latin incubō (“nightmare, one who lies down on the sleeper”), from incubō (“to lie upon, to hatch”, from in- (“on”) + cubō (“to lie down”)).