The antonym for "un-stopped" is "stopped." When we say something is "un-stopped," it means that it isn't blocked or clogged, and things can flow smoothly. For instance, we might say that a drain is un-stopped after being cleared. The opposite of un-stopped is obviously stopped, which means that something is obstructed, hindered or shut off. When a drain is stopped up, water cannot flow freely. Other antonyms for "un-stopped" are blocked, closed, obstructed, sealed, or plugged. These words describe something that is hindered or impeded in some way and cannot function as it should.