entropy

American  

[en-truh-pee] / ˈɛn trə pi /

noun

1. Thermodynamics.

   1. (on a macroscopic scale) a function of thermodynamic variables, as temperature, pressure, or composition, and differing from energy in that energy is the ability to do work and entropy is a measure of how much energy is not available. The less work that is produced, the greater the entropy, so when a closed system is void of energy, the result is maximum entropy.

   2. (in statistical mechanics) a measure of the randomness of the microscopic constituents of a thermodynamic system. S

2. (in data transmission and information theory) a measure of the loss of information in a transmitted signal or message.

3. (in cosmology) a hypothetical tendency for the universe to attain a state of maximum homogeneity in which all matter is at a uniform temperature heat death.

4. a state of disorder, or a tendency toward such a state; chaos.

5. a doctrine of inevitable social decline and degeneration.

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entropy British  

/ ˈɛntrəpɪ /

noun

1.  S.  a thermodynamic quantity that changes in a reversible process by an amount equal to the heat absorbed or emitted divided by the thermodynamic temperature. It is measured in joules per kelvin See also law of thermodynamics

2. a statistical measure of the disorder of a closed system expressed by S = k log P + c where P is the probability that a particular state of the system exists, k is the Boltzmann constant, and c is another constant

3. lack of pattern or organization; disorder

4. a measure of the efficiency of a system, such as a code or language, in transmitting information

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entropy Scientific  

/ ĕn′trə-pē /

1. A measure of the amount of energy in a physical system not available to do work. As a physical system becomes more disordered, and its energy becomes more evenly distributed, that energy becomes less able to do work. For example, a car rolling along a road has kinetic energy that could do work (by carrying or colliding with something, for example); as friction slows it down and its energy is distributed to its surroundings as heat, it loses this ability. The amount of entropy is often thought of as the amount of disorder in a system.

2. See also heat death

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entropy Cultural  

1. A measure of the disorder of any system, or of the unavailability of its heat energy for work. One way of stating the second law of thermodynamics — the principle that heat will not flow from a cold to a hot object spontaneously — is to say that the entropy of an isolated system can, at best, remain the same and will increase for most systems. Thus, the overall disorder of an isolated system must increase.

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Usage

What is entropy? Entropy is a measure of the amount of energy that is unavailable to do work in a closed system. In science, entropy is used to determine the amount of disorder in a closed system. We have a closed system if no energy from an outside source can enter the system. For example, an ice cube is orderly because all of its energy (heat) is tightly packed together. As the ice melts, its energy spreads out, creating disorder. The ice cube’s entropy is increasing as the ice melts into the more disorderly state of a liquid (in this case, water). In everyday use, entropy is used more broadly to refer to a lack of pattern or an increasing disorder, as in The coach’s disorganization spread throughout the team, creating some serious entropy at soccer practice. Example: My clean room quickly fell into entropy after my younger brother and sister had a chaotic pillow fight in it.

Discover More

Entropy is often used loosely to refer to the breakdown or disorganization of any system: “The committee meeting did nothing but increase the entropy.”

In the nineteenth century, a popular scientific notion suggested that entropy was gradually increasing, and therefore the universe was running down and eventually all motion would cease. When people realized that this would not happen for billions of years, if it happened at all, concern about this notion generally disappeared.

Other Word Forms

• entropic adjective

Etymology

Origin of entropy

First recorded in 1865; from German Entropie; from en- ² + trop(o)- + -y ¹

Explanation

The idea of entropy comes from a principle of thermodynamics dealing with energy. It usually refers to the idea that everything in the universe eventually moves from order to disorder, and entropy is the measurement of that change. The word entropy finds its roots in the Greek entropia, which means "a turning toward" or "transformation." The word was used to describe the measurement of disorder by the German physicist Rudolph Clausius and appeared in English in 1868. A common example of entropy is that of ice melting in water. The resulting change from formed to free, from ordered to disordered increases the entropy.

Example Sentences

"To understand and improve water-splitting devices, we need to consider not just energy, but entropy -- and how electric fields reshape the molecular landscape of water."

From Science Daily • Jan. 31, 2026

"He was like, 'it's about atrophy and entropy and the forces of the universe'," he said.

From Barron's • Jan. 23, 2026

It would be easier to argue that the best defense against entropy is to stand athwart any change in taste and manners, as Plato advised in the “Republic.”

From The Wall Street Journal • Jan. 9, 2026

Based on this picture, it seems reasonable to assume that the disorder of the system, known as entropy, should change between the early parton phase and the later hadron phase.

From Science Daily • Jan. 5, 2026

I try not to succumb to the crazy entropy of this thing between us.

From "The Sun Is Also a Star" by Nicola Yoon