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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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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

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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.

Theoretical models had predicted that the molecule could exist in two equally likely structures.

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

That causes the molecule to crack into hydrogen and ethylene, the basic building block of plastics such as polyethylene.

From The Wall Street Journal • Apr. 5, 2026

Their combined insights highlight a growing global effort to understand how this small molecule may support healthier aging and help protect against conditions like Alzheimer's and Parkinson's disease.

From Science Daily • Mar. 24, 2026

Over a barely digested lunch, the three scientists realized that this intermediate molecule had to shuttle from the cell’s nucleus, where genes were stored, to the cytoplasm, where proteins were synthesized.

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.