The general meaning of energy is the ability to be active. If you have a lot of energy, it means you like to be active. If you plan a low-energy day, it means a day of lounging around.

Energy is from Greek energeia "activity, operation," from energos "active, effective," from en "in" plus ergon "work." Specialized senses of the word energy include the power that comes from sources such as heat or electricity, and the ability of sources such as heat or light to do work. In physics, an erg is the centimeter-gram-second unit used to measure the amount of energy or the amount of work done.

Primary Meanings of energy

forceful exertion
an imaginative lively style (especially style of writing)
any source of usable power
Full Definitions of energy

n forceful exertion

“he plays tennis with great energy
vigor, vigour, zip
athleticism, strenuosity
intense energy
Type of:
force, forcefulness, strength
physical energy or intensity

n enterprising or ambitious drive

“Europeans often laugh at American energy
get-up-and-go, push
second wind
renewed energy or strength to continue an undertaking
Type of:
the trait of being highly motivated

n a healthy capacity for vigorous activity

“jogging works off my excess energy
vim, vitality
energetic vitality
ch'i, chi, ki, qi
the circulating life energy that in Chinese philosophy is thought to be inherent in all things; in traditional Chinese medicine the balance of negative and positive forms in the body is believed to be essential for good health
Type of:
good health, healthiness
the state of being vigorous and free from bodily or mental disease

n an imaginative lively style (especially style of writing)

“his writing conveys great energy
muscularity, vigor, vigour, vim
verve, vitality
an energetic style
light, spark, sparkle, twinkle
merriment expressed by a brightness or gleam or animation of countenance
Type of:
life, liveliness, spirit, sprightliness
animation and energy in action or expression

n any source of usable power

“the DOE is responsible for maintaining the energy policy”
Type of:
physical phenomenon
a natural phenomenon involving the physical properties of matter and energy

n (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work; the units of energy are joules or ergs

energy can take a wide variety of forms”
free energy
show 32 types...
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activation energy, energy of activation
the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur
alternative energy
energy derived from sources that do not use up natural resources or harm the environment
atomic energy, nuclear energy
the energy released by a nuclear reaction
binding energy, separation energy
the energy required to separate particles from a molecule or atom or nucleus; equals the mass defect
chemical energy
that part of the energy in a substance that can be released by a chemical reaction
electrical energy, electricity
energy made available by the flow of electric charge through a conductor
energy level, energy state
a definite stable energy that a physical system can have; used especially of the state of electrons in atoms or molecules
rest energy
the energy equivalent to the mass of a particle at rest in an inertial frame of reference; equal to the rest mass times the square of the speed of light
(physics) a manifestation of energy; the transfer of energy from one physical system to another expressed as the product of a force and the distance through which it moves a body in the direction of that force
heat, heat energy
a form of energy that is transferred by a difference in temperature
mechanical energy
energy in a mechanical form
radiant energy
energy that is transmitted in the form of (electromagnetic) radiation; energy that exists in the absence of matter
energy that is radiated or transmitted in the form of rays or waves or particles
AC, alternating current, alternating electric current
an electric current that reverses direction sinusoidally
atomic power, nuclear power
nuclear energy regarded as a source of electricity for the power grid (for civilian use)
ionizing radiation
high-energy radiation capable of producing ionization in substances through which it passes
cosmic radiation
radiation coming from outside the solar system
DC, direct current, direct electric current
an electric current that flows in one direction steadily
an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes
electromagnetic radiation, electromagnetic wave, nonparticulate radiation
radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge
geothermal energy
energy derived from the heat in the interior of the earth
K.E., kinetic energy
the mechanical energy that a body has by virtue of its motion
heat of dissociation
the heat required for a fluid substance to break up into simpler constituents
heat of formation
the heat evolved or absorbed during the formation of one mole of a substance from its component elements
heat of solution
the heat evolved or absorbed when one mole of a substance is dissolved in a large volume of a solvent
heat of transformation, latent heat
heat absorbed or radiated during a change of phase at a constant temperature and pressure
specific heat
the heat required to raise the temperature of one gram of a substance one degree centigrade
luminous energy
the energy associated with visible light
P.E., potential energy
the mechanical energy that a body has by virtue of its position; stored energy
solar energy, solar power
energy from the sun that is converted into thermal or electrical energy
solar radiation
radiation from the sun
wind generation, wind power
power derived from the wind (as by windmills)
Type of:
physical phenomenon
a natural phenomenon involving the physical properties of matter and energy

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