"Like one struck dumb" is a phrase that describes being speechless or stunned. There are several synonyms that can be used to convey a similar meaning such as dumbfounded, flabbergasted, astonished, amazed, stunned, and rendered speechless. All these words express a sense of surprise or shock that leaves a person incapable of speaking. They can be used in various contexts such as when receiving shocking news, hearing an unexpected outcome, or witnessing a remarkable event. These synonyms add variety to a writer's language, and help in creating a vivid picture in the reader's mind of the protagonist's emotional experience.