Real Dictionary

cylinder
countable noun: A cylinder is an object with flat circular ends and long straight sides.

cylinder in American English
in geometry, a solid figure consisting of two parallel bases in the form of congruent, closed curves joined by a smooth, continuous, closed surface; specif., such a figure (right circular cylinder) having circular bases and a surface perpendicular to the
noun: a surface or solid bounded by two parallel planes and generated by a straight line moving parallel to the given planes and tracing a curve bounded by the planes and lying in a plane perpendicular or oblique to the given planes
transitive verb: to furnish with a cylinder or cylinders

cylinder in Automotive Engineering
noun: In an engine, a cylinder is a part with flat circular ends and long straight sides in which a piston moves backward and forward.

cylinder in British English
noun: a solid consisting of two parallel planes bounded by identical closed curves, usually circles, that are interconnected at every point by a set of parallel lines, usually perpendicular to the planes. Volume base area × length

cylinder in Mechanical Engineering
noun: A cylinder is a cavity of circular cross-section that contains a moving piston, for example in an internal combustion engine.