# entropy

## noun

en·​tro·​py
plural entropies
1
thermodynamics : a measure of the unavailable energy in a closed thermodynamic system that is also usually considered to be a measure of the system's disorder, that is a property of the system's state, and that varies directly with any reversible change in heat in the system and inversely with the temperature of the system
broadly : the degree of disorder or uncertainty in a system
2
a
: the degradation of the matter and energy in the universe to an ultimate state of inert uniformity
Entropy is the general trend of the universe toward death and disorder.James R. Newman
b
: a process of degradation or running down or a trend to disorder
The deterioration of copy editing and proof-reading, incidentally, is a token of the cultural entropy that has overtaken us in the postwar years.John Simon
4
statistical mechanics : a factor or quantity that is a function of the physical state of a mechanical system and is equal to the logarithm of the probability for the occurrence of the particular molecular arrangement in that state
5
communication theory : a measure of the efficiency of a system (such as a code or a language) in transmitting information, being equal to the logarithm of the number of different messages that can be sent by selection from the same set of symbols and thus indicating the degree of initial uncertainty that can be resolved by any one message

## Did you know?

With its Greek prefix en-, meaning "within", and the trop- root here meaning "change", entropy basically means "change within (a closed system)". The closed system we usually think of when speaking of entropy (especially if we're not physicists) is the entire universe. But entropy applies to closed systems of any size. Entropy is seen when the ice in a glass of water in a warm room melts—that is, as the temperature of everything in the room evens out. In a slightly different type of entropy, a drop of food coloring in that glass of water soon spreads out evenly. However, when a nonphysicist uses the word, he or she is usually trying to describe a large-scale collapse.

## Examples of entropy in a Sentence

Recent Examples on the Web The reason that entropy increases for ordinary objects is not some inherent entropy-increasing tendency, which could somehow be reversed. Jennifer Ouellette and Sean M. Carroll, Ars Technica, 24 Nov. 2023 The higher the entropy of a word, the higher the information gain. Manon Bischoff, Scientific American, 28 Apr. 2023 Black holes have a surprising property: their entropy is proportional to their surface area, not their volume. Popular Mechanics, 31 July 2023 So the second law of thermodynamics tells us that entropy or disorder increases into the future. Steven Strogatz, Quanta Magazine, 22 Feb. 2023 Not least of these is whether the entropy of the universe is comparable to the potential number of biological microstates. The Physics Arxiv Blog, Discover Magazine, 29 Apr. 2022 No entanglement entropy means no entanglement; measuring B reveals nothing about A. High entanglement entropy means a lot of entanglement; measuring B teaches you a lot about A. Over dessert, Skinner and Nahum took this thinking two steps further. Charlie Wood, Quanta Magazine, 11 Sep. 2023 Saturday, a fire alarm at the AMC Burbank 16 caused an evacuation and cascading entropy. Miles Klee, Rolling Stone, 23 July 2023 Often thought of as the amount of disorder in a system, entropy is related to the system’s amount of useful energy: the higher the entropy, the less energy available. James Riordon, Scientific American, 24 May 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'entropy.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

## Word History

Etymology

International Scientific Vocabulary en- entry 2 + Greek tropē change, literally, turn, from trepein to turn

First Known Use

1867, in the meaning defined at sense 1

Time Traveler
The first known use of entropy was in 1867

entropy

## Cite this Entry

“Entropy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/entropy. Accessed 6 Dec. 2023.

## Medical Definition

entropy

noun
en·​tro·​py
plural entropies
: a measure of the unavailable energy in a closed thermodynamic system that is also usually considered to be a measure of the system's disorder and that is a property of the system's state and is related to it in such a manner that a reversible change in heat in the system produces a change in the measure which varies directly with the heat change and inversely with the absolute temperature at which the change takes place
broadly : the degree of disorder or uncertainty in a system