The Collaborative International Dictionary of English v.0.48:

Cusp \Cusp\ (k[u^]sp), n. [L. cuspis, -idis, point, pointed
   end.]
   [1913 Webster]
   1. (Arch.) A triangular protection from the intrados of an
      arch, or from an inner curve of tracery.
      [1913 Webster]

   2. (Astrol.) The beginning or first entrance of any house in
      the calculations of nativities, etc.
      [1913 Webster]

   3. (Astron) The point or horn of the crescent moon or other
      crescent-shaped luminary.
      [1913 Webster]

   4. (Math.) A multiple point of a curve at which two or more
      branches of the curve have a common tangent.
      [1913 Webster]

   5. (Anat.) A prominence or point, especially on the crown of
      a tooth.
      [1913 Webster]

   6. (Bot.) A sharp and rigid point.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cusp \Cusp\, v. t. [imp. & p. p. Cusped (k[u^]spt); p. pr. &
   vb. n. Cusping.]
   To furnish with a cusp or cusps.
   [1913 Webster] cuspate

V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006):

CUSP
       Commonly Used System Program (DEC)