An onerous task is a difficult and unpleasant job that requires a lot of effort. It is often referred to as a CHORE, which is a five-letter word. Onerous tasks can involve physical labor, such as cleaning or yard work, or mental labor, such as studying for a test or writing a paper. They can also involve tedious tasks, such as filling out paperwork or organizing files. Regardless of the type of task, it is usually unpleasant and time-consuming.