The word "slowed up" refers to the act of decreasing or diminishing the speed or pace of something. Its antonyms would be words that describe the opposite, which is to accelerate or speed up. Examples of antonyms for "slowed up" include rapid, hastened, brisk, quickened, and surged. Other terms that can be used interchangeably with these antonyms include expedited, advanced, and propelled. Depending on the context and usage of the word, different antonyms can be appropriate. In general, however, "slowed up" refers to a negative or hindering state, while its antonyms connote positivity or progress.