efficiency

noun

ef·​fi·​cien·​cy i-ˈfi-shən-sē 

plural efficiencies

1

: the quality or degree of being efficient

2

a

: efficient operation

b(1)

: effective operation as measured by a comparison of production with cost (as in energy, time, and money)

(2)

: the ratio of the useful energy delivered by a dynamic system to the energy supplied to it

3

: efficiency apartment

Synonyms of efficiency

• efficacy
• effectiveness
• efficaciousness

Examples of efficiency in a Sentence

Because of her efficiency, we got all the work done in a few hours.

The factory was operating at peak efficiency.

A furnace with 80 percent fuel efficiency wastes 20 percent of its fuel.

The company is trying to lower costs and improve efficiencies.

Recent Examples on the Web

Most of those efficiencies will be realized by the end of September. — Dade Hayes, Deadline, 14 Aug. 2026

With this new method, perovskite tandem solar cells achieved a power conversion efficiency of more than 29 percent. — Georgina Jedikovska, Interesting Engineering, 14 Aug. 2026

The most recent refresh included a shift towards using renewable energy and optimizing energy efficiency. — Mike Desimone, Robb Report, 14 Aug. 2026

The 1973 oil shock catalyzed investments in nuclear power, renewable energy, and efficiency that reduced the fossil-fuel intensity of the global economy even more rapidly than climate policy did in the years following the 2015 Paris Agreement. — Jason Bordoff, Foreign Affairs, 14 Aug. 2026

Word History

Etymology

borrowed from Latin efficientia, from efficient-, efficiens "producing or giving rise to something, immediate (of a cause), efficient" + -ia -y entry 2

First Known Use

1633, in the meaning defined at sense 1

Phrases Containing efficiency

• efficiency apartment
• efficiency expert
• hyper-efficiency

Rhymes for efficiency

• deficiency
• proficiency
• sufficiency
• immunodeficiency
• inefficiency
• insufficiency

Kids Definition

efficiency

noun

ef·​fi·​cien·​cy i-ˈfish-ən-sē 

plural efficiencies

1

: the quality or degree of being efficient

2

: efficient operation

3

: the ratio of the useful energy delivered by a machine to the energy supplied to it