Source : Webster's Revised Unabridged Dictionary (1913)

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

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

   {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} (Zo["o]l.), 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}.

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.

   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}.

   {Bow compasses}. See {Bow-compass}.

   {Caliber compasses}, {Caliper compasses}. See {Calipers}.

   {Proportional}, {Triangular}, etc., {compasses}. See under
      {Proportional}, etc.

Source : WordNet®

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: involving three parties or elements; "the triangular
        mother-father-child relationship"; "a trilateral
        agreement"; "a tripartite treaty"; "a tripartite
        division"; "a three-way playoff" [syn: {trilateral}, {tripartite},
         {three-party}, {three-way}]
     3: having three sides; "a trilateral figure" [syn: {trilateral},
         {three-sided}]