A 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.
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.
A group of two or more people, machines etc. working together; close collaboration.
A method of languagelearning based on mutual exchange, where ideally each learner is a native speaker in the language the other person wants to learn.