The term 'BIG HEADACHE' can be summarized by the crossword solution 'HASSLE', which is a 6-letter word. A HASSLE is an annoying, difficult, or troublesome situation that causes stress and frustration. It is often used to describe a situation that is time-consuming and requires a lot of effort. In this case, the term 'BIG HEADACHE' is referring to a situation that is particularly difficult and stressful.