Normal
When we know that norma is the Latin word for T-square and that normalis means perpendicular, we know almost all that must be known about the area in which the meaning of the terms “norm” and “normal” originated…. A norm, or rule, is what can be used to right, to square, to straighten… to impose a requirement on an existence.
—Georges Canguilhem, The Normal and the Pathological (1978), 239.