A thankless task is defined as a task that is not appreciated or acknowledged, despite the effort put into it. Synonyms for this phrase can include an unappreciated task, an unrewarding chore, an ungrateful duty, or an unsung job. Other alternatives include tedious work, grueling labor, thankless responsibility, and unacknowledged labor. These synonyms all describe a task that lacks recognition or praise and can be emotionally draining for those who undertake it. It is essential to acknowledge and give credit to those who undertake these tasks, as they are an important contribution to any organization or community.