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efficiency

n.
US //ɪˈfɪʃənsi// UK //ɪfˈɪʃənsi// ef·fi·cien·cy
  1. 1 avoiding waste (n.)
    B2 Upper Intermediate

    the ability to do something well and quickly without wasting time, money, or energy.

    the state or quality of being efficient; the ability to achieve maximum productivity with minimum wasted effort or expense.

    Example

    The new heating system has much better energy efficiency than the old one.

    Example

    The consultancy firm was hired to improve the operational efficiency of the factory by streamlining the assembly line process.

    Usage

    Often used with the preposition 'of' when referring to a specific resource, such as 'efficiency of fuel'.
  2. 2 physics/engineering (n.)
    C1 Advanced Technical Science

    the ratio of useful work or energy produced compared to the energy put in.

    the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in.

    Example

    Most car engines have a thermal efficiency of only about twenty-five percent.

    Example

    Engineers are constantly seeking to increase the aerodynamic efficiency of the aircraft to reduce fuel consumption during long-haul flights.

    Usage

    Usually expressed as a percentage or a decimal between 0 and 1.
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  1. 3 a small apartment (n.)
    C1 Advanced American English

    a small apartment that usually has only one main room for living and sleeping.

    a small, self-contained apartment, typically consisting of a single main room with a small kitchen area and a bathroom.

    Example

    He rented a small efficiency near the university to save money on rent.

    Example

    The building offers several efficiencies that are ideal for single professionals who prioritize a central location over square footage.

    Usage

    Commonly used in real estate listings in the United States.

    Teacher's tip

    Learners should note that 'studio apartment' is more common globally, while 'efficiency' is specifically American.
  2. 4 power to produce an effect (n.)
    C2 Proficiency Archaic Formal

    the power or ability to produce a specific result.

    the capacity or power to produce a desired effect or result.

    Example

    The old books spoke of the efficiency of certain herbs in curing fevers.

    Example

    The philosopher questioned the efficiency of the law in truly changing human behaviour rather than merely punishing it.

    Usage

    In modern English, 'efficacy' is almost always preferred for this meaning.

    Teacher's tip

    This sense is rarely encountered in modern speech; advise students to use 'efficacy' for the power of a medicine or treatment.
Origin

From Latin efficientia, equivalent to efficient + -cy.

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