Containment is the work of keeping something in, so it does not spread or grow stronger. With a fire, dirty oil in the sea, or a sickness, containment means: find it, hold the line, stop the next house or the next person from being hit. You will hear 'containment measures' in health news — not always a cure, often a pause. In older political English, especially the years of the Cold War, containment was the US idea of stopping another country's power from spreading without always fighting a huge war. Nuclear plants sit inside a thick containment building, a shell whose job is to keep danger in if the inside fails. Though actually, people stretch the word to any plan that holds a problem down rather than wiping it out: damage containment, crisis containment. The picture is the same: keep it inside the circle. Do not mix this with a container, which is only the box or bottle.