Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 n. A rate of inclination; a slope.
 n. An ascending or descending part; an incline.
 n. Physics The rate at which a physical quantity, such as temperature or pressure, increases or decreases relative to change in a given variable, especially distance.
 n. Mathematics A vector having coordinate components that are the partial derivatives of a function with respect to its variables.
 n. Biology A series of progressively increasing or decreasing differences in the growth rate, metabolism, or physiological activity of a cell, organ, or organism.
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. A slope or incline.
 n. A rate of inclination or declination of a slope.
 n. Of a function y = f(x) or the graph of such a function, the rate of change of y with respect to x, that is, the amount by which y changes for a certain (often unit) change in x.
 n. The rate at which a physical quantity increases or decreases relative to change in a given variable, especially distance.
 n. A vector operator that maps each value of a scalar field to a vector equal to the greatest rate of change of the scalar. Notation for a scalar field φ: φ
from the GNU version of the Collaborative International Dictionary of English
 adj. Moving by steps; walking.
 adj. Rising or descending by regular degrees of inclination.
 adj. Adapted for walking, as the feet of certain birds.
 n. The rate of regular or graded ascent or descent in a road; grade.
 n. A part of a road which slopes upward or downward; a portion of a way not level; a grade.
 n. The rate of increase or decrease of a variable magnitude, or the curve which represents it.
 n. The variation of the concentration of a chemical substance in solution through some linear path; also called concentration gradient;  usually measured in concentration units per unit distance. Concentration gradients are created naturally, e.g. by the diffusion of a substance from a point of high concentration toward regions of lower concentration within a body of liquid; in laboratory techniques they may be made artificially.
from The Century Dictionary and Cyclopedia
 Moving by steps; walking; gressorial: ambulatory: opposed to saltatory: said either of animals or of their gait: in heraldry, said of a tortoise used as a bearing and represented in fesse.
 In herpetology, walking or running on legs; specifically, of or pertaining to the Gradientia: correlated with salient and serpent.
 Rising or descending by regular degrees of inclination: as, the gradient line of a railroad.
 n. Same as grade, 2.
 n. In physics, the rate at which a variable quantity, as temperature or pressure, changes in value: as, thermometric gradient; barometric gradient.
 n. In mathematics, a rational integral homogeneous and isobaric function.
 n. In geometry, slope.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 n. the property possessed by a line or surface that departs from the horizontal
 n. a graded change in the magnitude of some physical quantity or dimension
Etymologies
Examples

And beneath this gradient is a scale of inborn ability, which is what gives the syllogism its unique potency.

I also think it might look a little strange if the bluetored gradient is the same.

(Most commonly however, the word gradient is used as applying to rates of conversion in terms of space.)

Since the slope of the line resembles an inclined plane, or what we call when we are climbing a hill a “grade,” many sciences use the word gradient to indicate this relationship.

This gradient is part of a big collection called ColorData [ "Gradients"].

In the backprojection technique, a magnetic field gradient is applied at several defined angles around an object, and the NMR spectrum recorded.
The Nobel Prize in Physiology or Medicine 2003  Perspectives

The resulting pH gradient is utilized by another membranebound protein, ATPase, to synthesize ATP, a compound used as a fuel in energydemanding biological processes.

As a result, an electrochemical proton gradient is created across the membrane.

Tweaked title gradient to be less abrupt (may not have worked)

This soggy to toasty divide  scientists call it a "gradient"  is part of what causes California's coastal fog.
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