[n] the amount by which something decreases [n] a process of becoming smaller or shorter
decrease, decrease
growth, increase, increase, increment, increment
abatement, ablation, abridgment, alleviation, attenuation, attrition, consumption, contraction, corrosion, curtailment, cut, cutting, dampening, damping, decrease, decrescence, deduction, deflation, deliquescence, depletion, depreciation, depression, dero