The Collaborative International Dictionary of English v.0.48:

Slope \Slope\, n. [Formed (like abode fr. abide) from OE.
   slipen. See Slip, v. i.]
   1. An oblique direction; a line or direction including from a
      horizontal line or direction; also, sometimes, an
      inclination, as of one line or surface to another.
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   2. Any ground whose surface forms an angle with the plane of
      the horizon.
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            buildings the summit and slope of a hill.
                                                  --Macaulay.
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            Under the slopes of Pisgah.           --Deut. iv.
                                                  49. (Rev.
                                                  Ver.).
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   3. The part of a continent descending toward, and draining
      to, a particular ocean; as, the Pacific slope.
      [Webster 1913 Suppl.]

   Note: A slope, considered as descending, is a declivity;
         considered as ascending, an acclivity.
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   Slope of a plane (Geom.), the direction of the plane; as,
      parallel planes have the same slope.
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