Lewis & Short

2. incŭbo, ōnis, m. [1. incubo], one who lies upon any thing.

  1. I. A spirit that watches over buried treasures (post-class.): cum modo incuboni pileum rapuisset, thesaurum invenit, Petr. Fragm. Trag. 38, 8.
  2. II. The nightmare, incubus (post-class.): ab incubone deludi, Scrib. Comp. 100: de incubone praesumptio, Tert. Anim. 44.