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

Frying is an art, perhaps plied nowhere with such efficiency and aplomb as at this lively lunch counter, where the very air seems to crackle and the scent of pork incites the blood. —Ligaya Mishan, New York Times, 11 May 2026

Some experts recommend keeping your AC no more than 20°F cooler than outdoor temperatures to maximize system efficiency without sacrificing comfort. —Nafeesah Allen, Better Homes & Gardens, 10 May 2026

The wheels will provide excellent reliability and energy efficiency for traversing the Lunar surface, while the arms provide great dexterity to manipulate objects. —Christopher McFadden, Interesting Engineering, 10 May 2026

The bigger lesson from the Strait of Hormuz crisis is that efficiency may work in a stable world, but falls apart in an unstable one. —Victor Nian, Fortune, 10 May 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