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

His workload and efficiency have been invaluable, and demoting seems unlikely. — Chandler Rome, New York Times, 29 June 2026

Unfiltered water, Adams insists, leads to sediment buildup in your water heater, which shortens its lifespan and lessens its heating efficiency. — Quincy Bulin, Southern Living, 28 June 2026

As the system can mix and match these operating modes, all power sources can contribute simultaneously when maximum performance is needed, or operate separately when efficiency is the priority. — Rupendra Brahambhatt, Interesting Engineering, 28 June 2026

More broadly, the technology also reignites debates over how to balance learning efficiency against the risk of cheating. — John Liu, CNN Money, 27 June 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