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Efficiency

ih-FISH-un-see /ɪˈfɪʃənsi/

nounB2SATTOEFLIELTS

GeneralFormal

The state or quality of being efficient; in physics, the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in.

In thermodynamics, efficiency is always less than 100% for any real heat engine or process, a direct consequence of the second law of thermodynamics (due to unavoidable heat loss and entropy increase).

The story behind the word. The word 'efficiency' comes from the Latin verb 'efficere,' meaning 'to bring about' or 'to accomplish.' It's about getting things done, and doing them well, without wasting effort. Over time, it evolved to specifically mean the ratio of output to input, a concept that became incredibly important during the Industrial Revolution as people sought to optimize machines and processes.

Word relationships

Productivity: Rate at which goods/services are produced; 'efficiency' is about doing it with minimal waste.
Effectiveness: Degree to which something is successful in producing a desired result; 'efficiency' is about the cost/effort to achieve that result.
Economy: Careful management of resources; 'efficiency' is a measure of output per input.

Inefficiency: The state of not achieving maximum productivity with minimum wasted effort or expense.
Wastefulness: The act of using resources carelessly or extravagantly.

Commonly confused with

Effectiveness: Efficiency is doing things right (optimizing input/output), while effectiveness is doing the right things (achieving goals).

Word family

efficient (adjective): achieving maximum productivity with minimum wasted effort or expense
efficiently (adverb): in an efficient manner

Collocations

energy efficiency
fuel efficiency
improve efficiency
operational efficiency
thermal efficiency

Example sentences

"Modern solar panels have significantly improved their efficiency in converting sunlight into electricity." Discussing energy conversion.
"Implementing new software dramatically increased the team's efficiency, allowing them to complete tasks faster." In a business context.

Memory hook

EFFICIENCY: The EFFORT you put IN, compared to the FISH you CATCH. Output per Input

When not to use

As a general synonym for 'effectiveness' if the context doesn't involve a ratio of output to input. Something can be effective without being efficient (e.g., a very powerful but wasteful engine).

Fun facts

The theoretical maximum efficiency of a heat engine is given by the Carnot efficiency, which depends only on the temperatures of the hot and cold reservoirs.
Improving energy efficiency is a major goal in combating climate change.