a.  1.  Having three angles; having the form of a triangle.  
2.  (Bot.) Oblong or elongated, and having three lateral angles;

Adj.  1.  triangular  having three angles; forming or shaped like a triangle; "a triangular figure"; "a triangular pyrimid has a triangle for a base" 
2.  triangular  involving three parties or elements; "the triangular motherfatherchild relationship"; "a trilateral agreement"; "a tripartite treaty"; "a tripartite division"; "a threeway playoff"  
3.  triangular  having three sides; "a trilateral figure" Synonyms: threesided, trilateral 