orthogonal

Of two objects, at right angles; perpendicular to each other.

A chord and the radius that bisects it are orthogonal.

Of a pair of vectors: having a zero inner product; perpendicular.

The normal vector and tangent vector at a given point are orthogonal.

Of a square matrix: such that its transpose is equal to its inverse.

Of a linear transformation: preserving its angles.

Of grid graphs, board games and polyominoes: vertical or horizontal but not diagonal.

An orthogonal line.

All of the orthogonals in this painting display an understanding of linear perspective.