geartrain(n = noun.artifact) gear, gearing, power train, train - wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed; "the fool got his tie caught in the geartrain"
is a kind of wheelwork
is a part of engine
has particulars: epicyclic gear train, epicyclic train, reduction gear

   a connected set of rotating gears by which force is transmitted or motion or torque is changed. [WordNet 1.5]