The phrase "stumbling block" refers to an obstacle that hinders progress or prevents success. There are several synonyms that can be used to convey a similar meaning. One such synonym is "barrier," which indicates an obstruction that is difficult to overcome. Another synonym is "impediment," which suggests something that interferes with progress or slows down the pace of work. Additionally, "obstacle" is a word that captures the notion of something standing in the way of progress. Other possible synonyms for "stumbling block" include "hurdle," "roadblock," "difficulty," and "challenge." Each of these words emphasizes the idea of an obstacle that must be overcome in order to achieve a desired outcome.