The Collaborative International Dictionary of English v.0.48:

Occult \Oc*cult"\, a. [L. occultus, p. p. of occulere to cover
   up, hide; ob (see Ob-) + a root prob. akin to E. hell: cf.
   F. occulte.]
   Hidden from the eye or the understanding; invisible; secret;
   concealed; unknown.
   [1913 Webster]

         It is of an occult kind, and is so insensible in its
         advances as to escape observation.       --I. Taylor.
   [1913 Webster]

   Occult line (Geom.), a line drawn as a part of the
      construction of a figure or problem, but not to appear in
      the finished plan.

   Occult qualities, those qualities whose effects only were
      observed, but the nature and relations of whose productive
      agencies were undetermined; -- so called by the schoolmen.


   Occult sciences, those sciences of the Middle Ages which
      related to the supposed action or influence of occult
      qualities, or supernatural powers, as alchemy, magic,
      necromancy, and astrology.
      [1913 Webster]