The antonyms for the word "step-up" include "decrease," "diminish," "reduce," "lower," "dwindle," and "abate." These terms all refer to the opposite of "step-up," which is to increase or improve something. When we decrease something, we make it smaller or less than before; when we diminish something, we make it less important or valuable; when we reduce something, we make it less in amount or size; when we lower something, we make it less in height or value; when we dwindle something, we make it smaller gradually; and when we abate something, we make it less intense or severe. These antonyms are essential in understanding the contrast between a step-up and a decrease in different contexts.