The term TOUGH TASK can be broken down into two crossword solutions: ONUS (4 letters) and NOPICNIC (8 letters). ONUS is a Latin word meaning 'burden' or 'RESPONSIBILITY'. It is often used to refer to the obligation of someone to fulfill a task or duty. NOPICNIC is an idiom which means that something is difficult or challenging. It is derived from the phrase 'no picnic', which implies that something is not easy or enjoyable. Together, these two words describe a situation that is difficult and requires a great deal of effort.