The term 'SOURCE OF TROUBLE' can be summarized by two crossword solutions: 'BANE' (4 letters) and 'HORNETSNEST' (11 letters). 'BANE' is an old English word meaning 'a cause of ruin, distress, or annoyance'. It is often used to describe something that is a source of great trouble or difficulty. 'HORNETSNEST' is a metaphor for a situation that is chaotic and full of conflict. It is usually used to describe a situation that is difficult to resolve due to the presence of many conflicting parties. Both terms are used to describe a situation that is causing trouble or distress.