problem

noun:a matter or situation regarded as unwelcome, harmful, or wrong and needing to be dealt with and overcome
- The main problem with the car is its faulty transmission.
noun:a question proposed for solution or discussion, especially in mathematics or science
- The students were asked to solve a difficult algebra problem.
adjective:denoting a person or group that is difficult to deal with or causes trouble
- He was a problem child in school, often disrupting the class.