Suc·cu·bus n.; pl. Succubi
  1. A demon or fiend; especially, a lascivious spirit supposed to have sexual intercourse with the men by night; a succuba.  Cf. Incubus.
  2. Med. The nightmare. See Nightmare, 2.
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  succubus
       n : a female demon believed to have sexual intercourse with
           sleeping men [syn: succuba]
       [also: succubi (pl)]