Definitions
1.NounThe initial agent that is the cause of all things.
2.NounA machine, such as a water wheel or steam engine, that receives and modifies energy as supplied by some natural source or fuel and transforms it into mechanical work
3.NounTractor unit. Or, more specifically, the front part of a semi-trailer type truck, i.e., the tractor to which the trailer part attaches.
4.NounA military or heavy construction vehicle.
5.NounA person or thing that is seminal and influential.