Use the adjective condign to describe a fair and fitting punishment, like the condign clean-up work assigned to a group of students after they made a big mess.
There are two ways to correctly pronounce condign: "CON-dine" or "con-DINE." The word comes from Latin: con- means "together, altogether" and dignus means "worthy." So, something that is condign is deserved or appropriate. It especially applies to a punishment that is severe but just, meaning the punishment is appropriate for the crime.