a long circular chamber containing a piston which is driven by exploding gases, as in a combustion cylinder;DO NOT USE 'cylinder' alone to mean 'a long circular chamber containing a piston which drives fluid', such as a pump cylinder or cylinder type pump; 'a long circular chamber which collects fluid', such as an accumulator cylinder, or 'a long bottle for holding gases or dry fire suppression chemicals under pressure, such as a nitrogen cylinder or an ether cylinder