triangular

having three angles; forming or shaped like a triangle

• “a triangular figure”
• “a triangular pyrimid has a triangle for a base”

involving three parties or elements

• “the triangular mother-father-child relationship”
• “a trilateral agreement”
• “a tripartite treaty”
• “a tripartite division”
• “a three-way playoff”

having three sides

• “a trilateral figure”