Punitive describes inflicting a punishment. If someone takes punitive action against you, you'll probably whine and complain — you're in trouble and you're about to get punished.
An easy way to remember the meaning of punitive is that it looks like the word punish — both come from the Latin root word punire, "to inflict a penalty on." Punitive doesn't always refer to a person-to-person punishment, like a mom disciplining a child. It can also describe the unpleasant result of an action on a large scale, like the punitive effect higher taxes will have on the middle class.