droid vs engine

droid

noun
  • A person having the qualities of an android; one with few or no emotions or little personality, or who acts in an unthinking manner; a robot. 

  • A robot, especially one made with some physical resemblance to a human (an android). 

engine

noun
  • A person or group of people which influence a larger group; a driving force. 

  • Anything used to effect a purpose; any device or contrivance; an agent. 

  • A self-powered vehicle, especially a locomotive, used for pulling cars along a track. 

  • A large construction used in warfare, such as a battering ram, catapult etc. 

  • The part of a car or other vehicle which provides the force for motion, now especially one powered by internal combustion. 

  • A complex mechanical device which converts energy into useful motion or physical effects. 

  • A software or hardware system responsible for a specific technical task (usually with qualifying word). 

How often have the words droid and engine occurred in a corpus of books? (source: Google Ngram Viewer )