The Collaborative International Dictionary of English v.0.48:

Succuba \Suc"cu*ba\, n.; pl. Succubae. [NL., fr. L. succubare
   to lie under; sub under + cubare to lie down; cf. L. succuba,
   succubo, one who lies under another.]
   A female demon or fiend. See Succubus.
   [1913 Webster]

         Though seeming in shape a woman natural
         Was a fiend of the kind that succubae some call. --Mir.
                                                  for Mag.
   [1913 Webster]

WordNet (r) 3.0 (2006):

succuba
    n 1: a female demon believed to have sexual intercourse with
         sleeping men [syn: succubus, succuba]