entropy

noun

en·​tro·​py ˈen-trə-pē 

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

3

: chaos, disorganization, randomness

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

entropic

en-ˈtrō-pik  -ˈträ-pik 

adjective

entropically

en-ˈtrō-pi-k(ə-)lē 

-ˈträ-

adverb

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

In the context of AI, entropy quantifies the variability and richness of information within a dataset, reflecting how evenly distributed or diverse the data points are across possible outcomes. —Hamilton Mann, Forbes, 20 Dec. 2024

Overall, this reduces the entropy enough to brute-force guess 16-bit search spaces. —Ars Technica, 28 Jan. 2025

In this case, although the answers all used different vocabulary, their meanings were roughly similar—earning them a low semantic entropy score, which indicates the model’s response is likely to be reliable. —Bypakinam Amer, science.org, 19 June 2024

This is the island formula for the entanglement entropy of the Hawking radiation. —Ahmed Almheiri, Scientific American, 1 Sep. 2022

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

Medical Definition

entropy

noun

en·​tro·​py ˈen-trə-pē 

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

entropic

en-ˈtrōp-ik  -ˈträp- 

adjective

entropically

-i-k(ə-)lē 

adverb