molecule

American  

[mol-uh-kyool] / ˈmɒl əˌkyul /

noun

1. 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.

2. Chemistry. a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.

3. any very small particle.

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molecule British  

/ ˈmɒlɪˌkjuːl /

noun

1. the simplest unit of a chemical compound that can exist, consisting of two or more atoms held together by chemical bonds

2. a very small particle

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molecule Scientific  

/ mŏl′ĭ-kyo̅o̅l′ /

1. A group of two or more atoms linked together by sharing electrons in a chemical bond. Molecules are the fundamental components of chemical compounds and are the smallest part of a compound that can participate in a chemical reaction.

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molecule Cultural  

1. A combination of two or more atoms held together by a force between them. (See covalent bond and ionic bond.)

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Other Word Forms

Derived Forms

• submolecule
  noun
• supermolecule
  noun

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:

• formula unit vs. molecule

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.

Example Sentences

Roche’s anti-amyloid antibody trontinemab has a fragment that mimics the natural iron-shuttling molecule known as transferrin.

From Barron's • Jun. 3, 2026

These functional groups are especially important because they strongly influence how a molecule behaves and what properties it has.

From Science Daily • May 20, 2026

When exposed to a trigger -- such as a small amount of heat or a catalyst -- the molecule snaps back into its original form, releasing the stored energy as heat.

From Science Daily • May 15, 2026

If a big piece of gravel makes it to the top, or a new stable molecule comes together, call it a winner.

From The Wall Street Journal • May 15, 2026

He’d already showered at the mine, most likely, but Mom wouldn’t let him in the house if he had a molecule of coal anywhere on him.

From "October Sky" by Homer Hickam

Related Words

• fragment
• particle