The antonyms for the word "most ascending" are "most descending" or "most declining." These words refer to the opposite direction to ascend or climb, which is to descend or go down. For instance, if a plane is taking off, it starts ascending or going up, but if it lands, it starts descending or going down. Similarly, if a graph shows a steady increase in numbers, it is ascending, but if it shows a steady decrease, it is descending. Hence, when we say "most ascending," we imply the highest point in a climb, and its antonyms refer to the lowest point in a decline.