gradient
gra.di.ent \'gra-d-e--*nt\ n [L gradient-, gradiens, prp. of gradi] 1a: the rate of regular or graded ascent or descent : INCLINATION 1b: a part sloping upward or downward 2: change in the value of a quantity per unit distance in a specified direc tion {vertical temperature ~} 3: a graded difference in physiological activity along an axis (as of the b ody or an embryonic field)