To chain-smoke is to smoke cigarettes one right after another, lighting the next with almost no break — sometimes even from the last cigarette. It is a well-known informal verb. It usually sounds a little critical: people say it when the smoking feels heavy or restless, not when someone just has one cigarette after dinner. You might chain-smoke through a long night of work, or while waiting and worrying. There is no metal chain. The picture is a chain of cigarettes, one linked to the next.