opposite side

opposite side

[′äp·ə·zət ′sīd] (mathematics) One of two sides of a polygon with an even number of sides that have the same number of sides between them along either path around the polygon from one of the sides to the other. For a given vertex of a polygon with an odd number of sides, a side of the polygon that has the same number of sides between it and the vertex along either path around the polygon.