The term 'heavy burden' can be described by four crossword solutions: ONUS (4 letters), MILLSTONE (9 letters), LOAD (4 letters), and TOUGHROWTOHOE (13 letters). ONUS is a Latin word meaning a burden or responsibility, while MILLSTONE is an idiom referring to a burden that is difficult to bear. LOAD is a more general term for a burden, and TOUGHROWTOHOE is an American phrase meaning a difficult task. All of these words refer to the idea of a heavy burden, which is a responsibility or task that is difficult to manage.