engine

Noun

• an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
  • medieval engines of war
    

• a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks

• something used to achieve a purpose
  • an engine of change
    

• motor that converts thermal energy to mechanical work

Related words

• Synonyms: 
  locomotive , locomotive engine , railway locomotive