"Plugging away at" is a phrase commonly used to describe working hard or persistently at a task. There are several synonyms for this phrase that can be used to add variety and nuance to your writing. Some options to consider include toiling, striving, grinding, persevering, or laboring away at something. Each of these verbs can convey a slightly different tone or context, so it's important to choose the one that best fits your intended meaning. For example, "toiling" might suggest a sense of exhaustion or difficulty, while "grinding" may imply a relentless or repetitive effort. By incorporating these synonyms into your writing, you can add depth and texture to your language and avoid overusing the same words.