efficiency

efficiency — noun

1. how well a system, machine, or process converts resources such as energy, fuel,

1.nounB2
Definition

how well a system, machine, or process converts resources such as energy, fuel, or time into useful output — for example, a car engine that travels further on less petrol, or a factory that makes more products using fewer materials.

Example

The new heating system improved the factory's energy efficiency by nearly thirty percent.

collocation: energy efficiency

Faisal redesigned the delivery routes to increase fuel efficiency across the whole fleet.

collocation: fuel efficiency

Common collocations
  • energy efficiency
  • fuel efficiency
  • thermal efficiency
  • cost efficiency
  • improve efficiency
  • increase efficiency
  • reduce efficiency
  • high efficiency
  • low efficiency
Synonyms
  • effectiveness

    Effectiveness is about achieving the intended result; efficiency is about achieving it with minimal waste.

  • productivity

    Productivity focuses on the amount of output per unit of input over time, while efficiency focuses on reducing waste across any resource.

  • economy

    Economy in this sense emphasizes saving money or resources, often in a broader financial context.

Antonyms
  • inefficiency

    The direct opposite — wasteful use of resources.

Usage Note

Commonly modified by adjectives that specify the type of resource: 'energy efficiency', 'fuel efficiency', 'cost efficiency'. The preposition 'of' introduces the system or device being measured.

Common Mistakes

We need to improve the efficient of our machines.
We need to improve the efficiency of our machines.
'efficient' is an adjective; the noun form is 'efficiency'.
The new engine has more efficiency.
The new engine has higher efficiency.' or 'The new engine is more efficient.
'more efficiency' is grammatically possible but unnatural; use 'higher' or 'greater' with 'efficiency'.

2. how well a person or group carries out tasks in an organised, productive manner,

2.nounB1
Definition

how well a person or group carries out tasks in an organised, productive manner, making good use of time and avoiding wasted effort — for example, a kitchen team that serves hundreds of meals without falling behind.

Example

The new software helped the team work with greater efficiency and far fewer delays.

preposition: with + efficiency

Lucas admired the kitchen staff's efficiency during the busy lunch service at the hotel.

Common collocations
  • work efficiency
  • operational efficiency
  • office efficiency
  • improve efficiency
  • increase efficiency
  • with efficiency
  • efficiency in
  • greater efficiency
  • remarkable efficiency
Synonyms
  • effectiveness

    Effectiveness stresses whether a goal is achieved at all; efficiency stresses how well resources are used while achieving it.

  • competence

    Competence refers to having the necessary skill or ability; efficiency refers to the speed and economy with which work is done.

  • proficiency

    Proficiency implies advanced skill gained through practice; efficiency is more about process than skill level.

Antonyms
  • inefficiency

    The direct opposite — disorganised, time-wasting work.

  • disorganisation

    Disorganisation is a cause of low efficiency; the two are closely related but not synonymous.

Usage Note

Often combined with 'in' followed by a gerund or noun ('efficiency in handling complaints', 'efficiency in communication'). Can be modified by 'greater', 'higher', 'improved', or 'remarkable'.

Common Mistakes

She works with high efficient.
She works with high efficiency.
'efficient' is an adjective; after a preposition we need the noun 'efficiency'.
The efficiency of doing tasks is important.
Efficiency in doing tasks is important.
use 'in', not 'of', when describing the activity.

3. a specific step or practice introduced in a business or institution to cut down

3.nounB2
Definition

a specific step or practice introduced in a business or institution to cut down on wasted resources — for example, switching off equipment overnight or ordering supplies in larger batches.

Example

The company introduced several energy efficiencies that cut their electricity bill by almost half.

plural form: efficiencies

Obi suggested a simple efficiency — turning off the lights in unused rooms after six.

Common collocations
  • cost efficiencies
  • energy efficiencies
  • operational efficiencies
  • identify efficiencies
  • introduce efficiencies
  • list efficiencies
Synonyms
  • cost-saving measure

    More explicit about the financial motivation; 'efficiency' is broader and can refer to time or energy savings too.

  • improvement

    A general term; 'efficiency' specifically implies reducing waste rather than any kind of change.

  • optimisation

    Suggests a systematic, data-driven improvement to a process, whereas 'efficiency' can be a simpler practical change.

Antonyms
  • waste

    Waste is what efficiencies aim to eliminate — the opposite of a saving measure.

Usage Note

This is the only sense that is regularly used in the countable plural form ('efficiencies'). In business contexts it often appears in the phrase 'cost efficiencies' or 'operational efficiencies'.

Common Mistakes

We found an efficiency to reduce paper use.' (unidiomatic as countable)
We found a way to reduce paper use.' or 'We identified an efficiency that reduced paper use.
The countable use is most natural in formal business writing and often takes 'identify' or 'introduce'.

4. a calculated value, often expressed as a percentage, that compares the useful wo

4.nounC1
Definition

a calculated value, often expressed as a percentage, that compares the useful work delivered by a machine or system with the total energy it receives — for example, a motor that converts 80 % of its electrical power into motion.

Example

An electric car motor can reach an efficiency of over ninety percent on good roads.

pattern: an efficiency of + percentage

The engineers tested the new turbine's efficiency under different weather conditions for a month.

Common collocations
  • thermal efficiency
  • conversion efficiency
  • mechanical efficiency
  • efficiency of + percentage
  • efficiency drops
  • efficiency improves
  • peak efficiency
  • average efficiency
Synonyms
  • yield

    Yield refers to the amount produced, not the ratio of output to input. A system can have high yield but low efficiency if it uses huge inputs.

  • output ratio

    A descriptive phrase rather than a standard synonym; 'efficiency' is the standard technical term for this ratio.

  • performance

    Performance is a broader term covering speed, reliability, and other factors, not just the input-output ratio.

Usage Note

This technical sense is used almost exclusively in engineering, physics, and energy-industry contexts. The noun is often modified by a percentage value following 'of'. Frequently appears in the phrase 'thermal efficiency' (heat engines), 'conversion efficiency' (solar cells), or 'mechanical efficiency' (machinery).

5. a small apartment or flat where the sleeping, living, and cooking areas are all

5.nounB2
Definition

a small apartment or flat where the sleeping, living, and cooking areas are all in a single large space, with only the bathroom separated — especially common in American English, where the full term is 'efficiency apartment'.

Example

Felix rented a small efficiency near the university for his first year of graduate school.

US English: efficiency (apartment)

The building on Maple Street has twelve efficiencies and three larger one-bedroom units for families.

Common collocations
  • rent an efficiency
  • live in an efficiency
  • small efficiency
  • efficiency apartment
  • efficiency unit
Synonyms
  • studio apartment

    The more common term in both American and British English; 'efficiency' is slightly older and more common in real-estate listings.

  • studio flat

    The British equivalent term.

  • bedsit

    A British term for a single room used as both bedroom and living room, usually with shared bathroom facilities — different from an efficiency which has a private bathroom.

Usage Note

Chiefly used in American English. In British English the equivalent is 'studio flat' or 'studio apartment'. The full form 'efficiency apartment' is also common in real-estate listings. This sense is always countable.

Common Mistakes

I live in an efficient.' (adjective used as noun)
I live in an efficiency.
'efficiency' is the noun; 'efficient' is the adjective and does not mean an apartment.

Word family

Synonym discussion

Sense: noun/2

Efficiency, effectiveness, productivity, and competence overlap but differ in focus. Efficiency is about doing things with minimal waste of time, energy, or resources — getting the most output from the least input. Effectiveness is about achieving the desired outcome, regardless of resource use: a sales team can be effective if it meets its targets even if it makes many expensive calls. Productivity specifically measures output per unit of time or labour, often in a workplace or economic context, such as how many units a worker produces per hour. Competence refers to having the skill and ability to perform a task well — a competent surgeon can perform a complex operation, but whether she does so quickly (efficiency) depends on other factors. In a sentence: 'The new hire is competent at her job, but the team's overall efficiency won't improve unless we also streamline the approval process.' Another example: 'The marketing campaign was effective — it reached a million viewers — but it was not efficient, because it cost twice the budget.'

efficiency ↗effectiveness ↗productivity ↗competence ↗

Common collocations

Nouns

Adverbs

Phrases

  • improve efficiency
  • increase efficiency
  • reduce efficiency
  • boost efficiency
  • achieve efficiency
  • efficiency gains
  • efficiency savings
  • efficiency improvements
  • lack of efficiency

Prepositions

Etymology

LatinFrenchEnglish

The word 'efficiency' comes from Latin 'efficientia', meaning 'efficacy, efficiency, power to produce an effect'. This in turn comes from 'efficere' ('to accomplish, bring about, produce'), which combines 'ex-' ('out') and 'facere' ('to do, make'). The word entered English through French 'efficacité' in the late 16th century, originally carrying the general meaning of 'the power to produce an effect'. Its modern sense of 'productive output relative to input' developed during the Industrial Revolution, when engineers needed a term to describe how well machines and factories converted fuel into useful work.