What's the difference between a motor and an engine? (2013)

Original Article ↗ Hacker News Discussion ↗

Scope of the distinction

  • Many participants say that in everyday English, “engine” and “motor” are often used interchangeably, especially for car powerplants.
  • Others insist they are not true synonyms, especially in technical or engineering contexts.
  • Several note that some collocations feel fixed: “jet engine,” “steam engine,” “fire engine,” “search engine,” but never “electric engine.”

Competing definitions

  • Energy source–based:
    • Common pattern: “engine” burns fuel or uses heat (internal/external combustion, heat engines); “motor” is electrical, hydraulic, pneumatic, or otherwise non-combustive.
    • Counterexamples: “rocket motor,” “motorway,” “motorcycle,” many of which involve combustion; so this rule is seen as leaky.
  • Function/role–based:
    • Some: motor = produces motion/locomotion; engine = produces power/work, possibly not motion.
    • Others: engine = self-contained, cyclic system driving a process; motor = specific component converting some energy into kinetic energy.
    • Several argue either:
      • motor ⊂ engine (motor = engine that changes momentum), or
      • engine ⊂ motor (engine = motor that’s a complex heat/combustion device).
    • No consensus; many acknowledge their own usage is intuitive and full of exceptions.

Domain-specific usage

  • Cars: many say “gas engine” vs “electric motor,” but “motor car,” “motorsport,” “blown motor” remain common.
  • Aviation: some mechanics use “engine” and “motor” interchangeably; “jet engine” is standard.
  • Marine: “outboard motor,” never “outboard engine.”
  • Rockets: one view—solid rockets = motors (no moving parts), liquid rockets = engines (pumps/valves); hobby industry labeling has blurred this.
  • Software: “database/game/search engine,” but not “software motor”; French translates “search engine” as “moteur de recherche” (“search motor”).

Cross-linguistic perspectives

  • Many languages (French, Spanish, German, Dutch, Italian, Polish, others) largely have a single everyday word that covers both “motor” and “engine,” plus separate terms like “machine” or “Triebwerk” for specific types.
  • “Engineer” is linked etymologically to “ingenium” (clever contrivance), tying “engine” historically to “contraption.”

Language evolution and prescription

  • Some argue treating older distinctions as binding is “prescriptivist” and unrealistic; actual usage makes them near-synonyms.
  • Others strongly resist phrases like “electric engine” and prefer keeping a technical distinction.
  • Broader debate branches into how language norms are set (academies vs actual usage), with “literally” cited as an example of long-standing semantic drift.