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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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:
The molecule, known as BRP, works through a different but related metabolic pathway and activates a separate group of neurons in the brain.
From Science Daily ● Jul. 24, 2026
Researchers led by Professor Ryuichi Tatsumi of Kyushu University's Faculty of Agriculture have identified a molecule that could protect and enhance an important signal involved in muscle repair.
From Science Daily ● Jul. 24, 2026
GLP-1 medications like Ozempic are also peptides: they mimic a naturally occurring molecule that regulates appetite, blood sugar and digestion.
From Barron's ● Jul. 23, 2026
Rather than reverse-engineering a large molecule, eCPs can hit the same biological target and produce the same clinical effect through a much simpler molecule.
From The Wall Street Journal ● Jul. 22, 2026
Hemoglobin A, the most intensively studied version of the molecule, is shaped like a four-leaf clover.
From "The Gene" by Siddhartha Mukherjee
They are naturally occuring in the body, signaling molecules that dictate major physiological processes like tissue repair or metabolism.
From Barron's ● Jul. 23, 2026
So-called small molecules, which are typically pills dispensed by pharmacies, have generics that are much cheaper in the U.S. than abroad because of the intense price competition that patent expiration unleashes.
From The Wall Street Journal ● Jul. 22, 2026
This is the idea behind antibiotic adjuvants, which are companion molecules that do not kill bacteria directly but instead restore the power of antibiotics.
From Science Daily ● Jul. 22, 2026
That these molecules are easier to manufacture matters greatly for competition: Small molecules are the drugs for which generic price competition has already proved so beneficial to patients.
From The Wall Street Journal ● Jul. 22, 2026
In liquid or gas form, molecules whiz dizzily in space, moving randomly, like particles of dust.
From "The Gene" by Siddhartha Mukherjee
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.
