The word "most mushrooming" means to grow or increase rapidly, but there are several antonyms to describe the opposite, slow or stagnant growth. Some antonyms for "most mushrooming" include decelerating, receding, dwindling, contracting, and shrinking. These words imply a decrease or decline in growth, rather than an increase. When the growth of something is decelerating, it means that it is slowing down or gradually coming to a halt. Receding implies a withdrawal or reduction of something. On the other hand, dwindling, contracting, and shrinking suggest a gradual decrease in size, shape or quantity. Overall, these antonyms are used to show the opposite of "most mushrooming" or rapid growth.