The Collaborative International Dictionary of English v.0.48:

Incubus \In"cu*bus\, n.; pl. E. Incubuses, L. Incubi. [L.,
   the nightmare. Cf. Incubate.]
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   1. A demon; a fiend; a lascivious spirit, supposed to have
      sexual intercourse with women by night. --Tylor.
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            The devils who appeared in the female form were
            generally called succubi; those who appeared like
            men incubi, though this distinction was not always
            preserved.                            --Lecky.
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   2. (Med.) The nightmare. See Nightmare.
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            Such as are troubled with incubus, or witch-ridden,
            as we call it.                        --Burton.
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   3. Any oppressive encumbrance or burden; anything that
      prevents the free use of the faculties.
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            Debt and usury is the incubus which weighs most
            heavily on the agricultural resources of Turkey.
                                                  --J. L.
                                                  Farley.
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