Definition of molecule in US English:



  • A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

    • ‘It works by affecting a molecule called nitric oxide, which expands blood vessels.’
    • ‘This electricity splits the water molecules in an electrolyte, producing hydrogen.’
    • ‘The reactant ions have enough energy to ionise the molecules of interest but not enough to break them up.’
    • ‘At the root of sunburn are damaging molecules, free radicals that increase when the skin gets too much sun.’
    • ‘In the water molecule there are three atoms: two of hydrogen and one of oxygen.’
    particle, bit, little bit, tiny bit, tiny piece, fragment, fraction, grain, granule, crumb, morsel, mite, mote, speck, spot, dot
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Late 18th century: from French molécule, from modern Latin molecula, diminutive of Latin moles ‘mass’.