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.

---

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

---

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.

---

molecule Cultural  

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

---

Other Word Forms

• submolecule noun
• supermolecule noun

Etymology

Origin of molecule

First recorded in 1785–95; earlier molecula, from New Latin, from Latin mōlē(s) “mass” ( 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

Chemists have achieved what many once considered impossible by stabilizing an extremely reactive molecule in water, confirming a 67-year-old theory about vitamin B1.

From Science Daily • Apr. 11, 2026

Instead of traveling freely, they hop from one molecule to another.

From Science Daily • Apr. 7, 2026

This molecule, known as the deprotonated dimer H3PO4·H2PO4-, became the focus of the study.

From Science Daily • Apr. 7, 2026

The key ingredient in Syngenta’s Virestina is a new molecule called metproxybicyclone, developed using machine-learning models.

From The Wall Street Journal • Apr. 6, 2026

If he were, Lydia would have asked him why he looked as though he felt like his heart was being pulled from his chest, fiber by fiber, cell by cell, molecule by molecule.

From "The Serpent King" by Jeff Zentner

Related Words

• fragment
• particle