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

Given what the rest of Europe endured, such benign civic efficiency verges on the comic. —Anthony Lane, New Yorker, 13 Apr. 2026

If extended to the Q06 platform, this chemistry could enhance cold-weather efficiency and provide a cost-competitive alternative to traditional lithium-ion configurations in select variants. —Bojan Stojkovski, Interesting Engineering, 12 Apr. 2026

The World Bank, in fact, attributes most of the drop in the global economy’s dependence on oil to stricter fuel efficiency requirements for vehicles around the world. —Paul Wiseman, Los Angeles Times, 12 Apr. 2026

And in three years, when the board asks why nobody internal was ready to step up, the answer is going to be sitting in that 2023 efficiency deck. —Kristien Turner, Fortune, 12 Apr. 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