Most taper refers to narrowing down or decreasing in size gradually. The antonym of most taper would be the opposite, which is to expand or increase in size. Some possible antonyms for most taper that could be used in different contexts include broaden, widen, fatten, grow, thicken, swell, and augment. These words suggest a growth or increase in width, girth or size. For example, an exercise to widen the upper body could be considered an antonym of a workout plan that aims to most taper the waistline. Similarly, adding more material to a piece of cloth can be considered an antonym of cutting it to most taper.