Grad, grade
Grade or grad comes from the Latin word, gradus, that means a 'step'. Grade
has always had a connotation of dividing a larger quantity or unit. In this
way grade has had the same meaning as degree.
The Oxford English Dictionary cites a 1593 definition when it defines
'Grade' as: 'Math. A degree; the 90th part of a right angle or quadrant'.
Note that this is a 1593 definition of the grade. Le Petit Robert defines grade from 1803 as *Centi�me partie d'un quadrant*.
The metric bible, 1998 edition lists the radian (symbol "rad") as "an SI derived unit". It lists the degree (of angle) as a "non-SI unit accepted for use with the International System". It does not list the grade, grad. or gon at all.
