molecule
n.-
1 chemical unit (n.) B2 Upper Intermediate Technical Sciencethe smallest part of a chemical substance that can exist on its own, made of two or more atoms.
the smallest particle of a specific element or compound that retains its chemical properties, consisting of two or more atoms held together by chemical bonds.
ExampleA water molecule is made of two hydrogen atoms and one oxygen atom.
ExampleThe researchers used an electron microscope to observe how each individual molecule reacted when exposed to the new catalyst.
UsageCountable noun in scientific contexts.
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2 a tiny amount (n.) C1 Advanced Literarya very small amount of something.
an infinitesimal or extremely small quantity of a substance or quality.
ExampleThere was not a single molecule of dust left in the clean room.
ExampleHe did not possess a single molecule of common sense, despite his impressive academic credentials.
Teacher's tipThis sense is often used in negative sentences to emphasize that something is completely missing.
Borrowed from French molécule, from New Latin molecula (“a molecule”), diminutive of Latin moles (“a mass”).