# 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 reduction of energy in the interactions between molecules outweighs the opposing contribution from entropy to stay evenly mixed. Trevor Grandpre, Scientific American, 14 Aug. 2024 This entropy, in turn, is proportional to the bit length of the modulus. Dan Goodin, Ars Technica, 9 Aug. 2024 But here, the fictional Tanaka Arena (a Toronto location standing in for Philadelphia) is a venue quite different, vaster and more hospitable to entropy, than a behind-glass cell at the Baltimore State Hospital for the Criminally Insane. Ryan Lattanzio, IndieWire, 2 Aug. 2024 The key is to measure this entanglement entropy in the presence of multiple copies of the system. Ahmed Almheiri, Scientific American, 1 Sep. 2022

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 14 Sep. 2024.

## 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