Troublesome means causing difficulty, annoyance, or worry. A troublesome situation is one that creates problems you have to deal with. When your teacher assigns a troublesome math problem, it's not impossible but it takes real effort and keeps tripping you up. A troublesome cough that won't go away might need a doctor's attention.

Something troublesome creates significant, persistent problems that demand attention. A troublesome neighbor might play loud music late at night, making it hard to sleep. A troublesome leak in the roof requires attention before it causes real damage. The word suggests an ongoing problem rather than a quick, one-time hassle.

People can be troublesome too. A troublesome student disrupts class repeatedly, making it harder for everyone to learn. A troublesome younger sibling might keep interrupting your homework or getting into your things. Notice that calling someone troublesome is fairly serious: it means they're creating real problems, not just being occasionally annoying. The difference matters because everyone has off days, but truly troublesome behavior is a pattern that significantly affects others.