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[mol-uh-kyool] /ˈmɒl əˌkyul/
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.
Chemistry. a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.
any very small particle.
Origin of molecule
1785-95; earlier molecula < New Latin, equivalent to Latin mōlē(s) mass + -cula -cule1
Related forms
submolecule, noun
supermolecule, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for molecules
  • This, as its name suggests, works out the weight of the molecules in each component.
  • molecules could one day work as quantum computers.
  • The trick to its absorbency is in the way those building-block molecules are arranged.
  • The molecules in such liquids are closely packed, but loosely arranged.
  • Researchers can attach the fluorescent molecules to a protein inside a dividing cancer cell or a spreading virus.
  • Because the molecules are larger than sodium and chlorine atoms, they do not stack as neatly.
  • But even gene scientists today say they are struggling with the many permutations of those four molecules.
  • Organic molecules inside space rock were probably the result of plain old chemistry.
  • molecules are constantly changing and rearranging their atoms in chemical reactions to form new molecules and compounds.
  • The molecules haven't yet achieved self-replication, the ultimate benchmark of life, but they hint at it.
British Dictionary definitions for molecules


the simplest unit of a chemical compound that can exist, consisting of two or more atoms held together by chemical bonds
a very small particle
Word Origin
C18: via French from New Latin mōlēcula, diminutive of Latin mōlēs mass, mole4
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
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Word Origin and History for molecules



1794, "extremely minute particle," from French molécule (1670s), from Modern Latin molecula, diminutive of Latin moles "mass, barrier" (see mole (3)). A vague meaning at first; the vogue for the word (used until late 18c. only in Latin form) can be traced to the philosophy of Descartes. First used of Modern Latin molecula in modern scientific sense by Amedeo Avogadro (1811).

Online Etymology Dictionary, © 2010 Douglas Harper
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molecules in Medicine

molecule mol·e·cule (mŏl'ĭ-kyōōl')
The smallest particle into which an element or a compound can be divided without changing its chemical and physical properties; a group of atoms that is held together chemically.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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molecules in Science
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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molecules in Culture
molecule [(mol-uh-kyoohl)]

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

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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