molecule
Americannoun
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Chemistry, Physics. the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound.
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Chemistry. a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.
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any very small particle.
noun
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the simplest unit of a chemical compound that can exist, consisting of two or more atoms held together by chemical bonds
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a very small particle
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of molecule
First recorded in 1785–95; earlier molecula, from New Latin, from Latin mōlē(s) “mass” ( cf. molar 2 ( def. )) + -cula -cule 1
Compare meaning
How does molecule compare to similar and commonly confused words? Explore the most common comparisons:
Explanation
A molecule is the simplest structural unit of a substance that still keeps the properties of that substance, like a molecule of water. This scientific word also gets used in unscientific ways, as in "Every single molecule in my body wants that chocolate cupcake!" People sometimes confuse molecules with atoms, but a molecule is made up of atoms. A molecule retains the characteristic of the substance it’s from, so a water molecule is still water. An atom only has the characteristics of its element, not the larger composition. For example, a water molecule, H2O, is made up of two hydrogen atoms and one oxygen atom.
Vocabulary lists containing molecule
Word Generation Science - Introductory Chemistry Concepts
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Words to Know Before You Defrost the Bird
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Cell Biology - Middle School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
To ensure the treatment reached prostate cancer cells, the team attached a targeting molecule that recognizes PSMA, a protein found on the surface of prostate tumor cells.
From Science Daily ● Jul. 9, 2026
Because the mirror image versions of the same molecule interact differently with the coatings, they move through the tubes at different speeds, allowing the instrument to separate them.
From Science Daily ● Jul. 9, 2026
To resolve the uncertainty, the Northwestern team relied on total synthesis, a process in which researchers build a natural molecule step by step in the laboratory.
From Science Daily ● Jul. 6, 2026
When paired with a donor molecule, the system reached an upconversion efficiency of 1.9%.
From Science Daily ● Jun. 26, 2026
From our first conversations we assumed that the DNA molecule contained a very large number of nucleotides linearly linked together in a regular way.
From "Double Helix" by James D. Watson
They also had lower indicators of oxidative stress, a form of cellular damage caused when unstable molecules known as reactive oxygen species overwhelm the body's protective systems.
From Science Daily ● Jul. 18, 2026
Humanin is among the most extensively studied of these molecules.
From Science Daily ● Jul. 18, 2026
Within a month, he had developed an elegant formula that would upend scientific understanding of how molecules use energy and eventually win him the Nobel Prize.
From Los Angeles Times ● Jul. 17, 2026
It describes how energy is released from the chemical reactions of molecules in the gas phase.
From Los Angeles Times ● Jul. 17, 2026
For the most part they drifted randomly like dust motes in a shaft of sunlight, or molecules in a glass of water.
From "The Amber Spyglass" by Philip Pullman
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.