The Collaborative International Dictionary of English v.0.48:

Triangulate \Tri*an"gu*late\, v. t. [imp. & p. p.
   Triangulated; p. pr. & vb. n. Triangulating.]
   1. To divide into triangles; specifically, to survey by means
      of a series of triangles properly laid down and measured.
      [1913 Webster]

   2. To make triangular, or three-cornered.
      [1913 Webster]