Definitions
1.nounA carriage pulled by two or more draught animals (generally draught horses) harnessed one behind the other, both providing the pulling power but only the animal in front able to steer.
2.noun(transferred sense) A bicycle or tricycle in which two people sit one behind the other, both able to pedal but only the person in front able to steer.
3.nounA group of two or more people, machines etc. working together; close collaboration.