Also, orthographic.pertaining to or involving right angles or perpendiculars: an orthogonal projection.
b.
(of a system of real functions) defined so that the integral of the product of any two different functions is zero.
c.
(of a system of complex functions) defined so that the integral of the product of a function times the complex conjugate of any other function equals zero.
d.
(of two vectors) having an inner product equal to zero.
e.
(of a linear transformation) defined so that the length of a vector under the transformation equals the length of the original vector.
f.
(of a square matrix) defined so that its product with its transpose results in the identity matrix.
2.
Crystallography. referable to a rectangular set of axes.
Origin: 1565–75; obsolete orthogon(ium) right triangle (< Late Latinorthogōnium < Greekorthogṓnion (neuter) right-angled, equivalent to ortho-ortho- + -gōnion-gon) + -al^{1}
from Fr. orthogonal, from orthogone, from L.L. orthogonius, from Gk. orthogonios "right-angled," from ortho- "straight" (see ortho-) + gonia "angle," related to gony "knee" (see knee).