1. 三角(形)的
Something that is triangular is in the shape of a triangle.

2. 三角关系的;三人间的;三方面的
You can describe a relationship or situation as triangular if it involves three people or things.

1. having three sides

e.g. a trilateral figure

Synonym: trilateralthree-sided

2. having three angles
forming or shaped like a triangle

e.g. a triangular figure
a triangular pyrimid has a triangle for a base