The Collaborative International Dictionary of English v.0.48:

Compasses \Com"pass*es\, n., pl.
   An instrument for describing circles, measuring figures,
   etc., consisting of two, or (rarely) more, pointed branches,
   or legs, usually joined at the top by a rivet on which they
   move.
   [1913 Webster]

   Note: The compasses for drawing circles have adjustable pen
         points, pencil points, etc.; those used for measuring
         without adjustable points are generally called
         dividers. See Dividers.
         [1913 Webster]

   Bow compasses. See Bow-compass.

   Caliber compasses, Caliper compasses. See Calipers.

   Proportional, Triangular, etc., compasses. See under
      Proportional, etc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Triangular \Tri*an"gu*lar\, a. [L. triangularis: cf. F.
   triangulaire.]
   1. Having three angles; having the form of a triangle.
      [1913 Webster]

   2. (Bot.) Oblong or elongated, and having three lateral
      angles; as, a triangular seed, leaf, or stem.
      [1913 Webster]

   Triangular compasses, compasses with three legs for taking
      off the angular points of a triangle, or any three points
      at the same time.

   Triangular crab (Zool.), any maioid crab; -- so called
      because the carapace is usually triangular.

   Triangular numbers (Math.), the series of numbers formed by
      the successive sums of the terms of an arithmetical
      progression, of which the first term and the common
      difference are 1. See Figurate numbers, under
      Figurate.
      [1913 Webster]

WordNet (r) 3.0 (2006):

triangular
    adj 1: having three angles; forming or shaped like a triangle;
           "a triangular figure"; "a triangular pyrimid has a
           triangle for a base"
    2: having three sides; "a trilateral figure" [syn: trilateral,
       triangular, three-sided]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "triangular":
   cuneate, cuneated, cuneiform, deltoid, fan-shaped, oxygonal, three,
   three-cornered, three-dimensional, three-footed, three-in-one,
   three-pronged, three-sided, triadic, trial, triangulate, triarch,
   trichotomous, tricorn, tricornered, tricuspid, trident, tridental,
   trifid, triflorate, triflorous, trifurcate, trigonal, trigonoid,
   trigrammatic, trihedral, trilateral, trimerous, trinal, trine,
   triparted, tripartite, triple, triplex, tripodic, triquetral,
   triquetrous, trisected, triune