Source: The Collaborative International Dictionary of English v.0.48
Succubus \Suc"cu*bus\, n.; pl. Succubi. [See Succuba.]
1. A demon or fiend; especially, a lascivious spirit supposed
to have sexual intercourse with the men by night; a
succuba. Cf. Incubus.
[1913 Webster]
2. (Med.) The nightmare. See Nightmare, 2.
[1913 Webster]