complication
n. C / Un. a new problem that makes a situation more difficult to deal with. In medicine, it is a second illness or medical problem that happens while you are already sick.
n. a secondary disease or condition aggravating an already existing one; more generally, a factor that makes a situation more complex or difficult to resolve.
The surgery was successful and there was no complication.
The doctor explained that the patient's high blood pressure could lead to a serious complication during the recovery process.
While the initial plan seemed straightforward, the sudden resignation of the lead architect introduced a complication that the project management team had not anticipated in their risk assessment.
Often used with the verbs 'arise' or 'develop'. In its medical sense, it is frequently used in the plural to describe post-operative risks.