Sizably, which means "to a considerable extent in size or amount," has several antonyms. Some of them include insignificantly, negligibly, slightly, meagerly, trivially, sliver, microscopically, tiny, and minutely. Insignificantly refers to something that's so small or trivial that it doesn't significantly impact anything, while negligibly has the same meaning but additionally suggests that the small size or amount is almost not noticeable. Slightly means a small degree, amount, or extent, while meagerly implies an inadequate or insufficient amount or size. Trivially refers to something that is trifling or lacks importance, while sliver and microscopically both suggest something that is incredibly small. Lastly, tiny and minutely both refer to things that are extremely small or insignificant.