An unwelcome task is a job or assignment that is not desired or wanted. The term 'ONUS' is a four-letter word that can be used to describe such a task. It is derived from the Latin phrase 'ONUS probandi, ' which translates to 'the burden of proof.' ONUS is often used in legal contexts to refer to the responsibility of proving a claim or allegation. In general, it can be used to refer to any unpleasant or unwanted obligation.