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.

Definitions of molecule
  1. noun
    (physics and chemistry) the simplest structural unit of an element or compound
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    dipole molecule
    a molecule that is a permanent dipole
    protein molecule
    any large molecule containing chains of amino acids linked by peptide bonds
    a small molecule (not a protein but sometimes a vitamin) essential for the activity of some enzymes
    EDTA, ethylenediaminetetraacetic acid
    a complex molecule used medically to chelate metal ions in cases of lead or heavy metal poisoning
    macromolecule, supermolecule
    any very large complex molecule; found only in plants and animals
    any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes
    carbohydrate, saccharide, sugar
    an essential structural component of living cells and source of energy for animals; includes simple sugars with small molecules as well as macromolecular substances; are classified according to the number of monosaccharide groups they contain
    cocarboxylase, thiamine pyrophosphate
    a coenzyme important in respiration in the Krebs cycle
    coenzyme A
    a coenzyme present in all living cells; essential to metabolism of carbohydrates and fats and some amino acids
    lipid, lipide, lipoid
    an oily organic compound insoluble in water but soluble in organic solvents; essential structural component of living cells (along with proteins and carbohydrates)
    NAD, nicotinamide adenine dinucleotide
    a coenzyme present in most living cells and derived from the B vitamin nicotinic acid; serves as a reductant in various metabolic processes
    NADP, nicotinamide adenine dinucleotide phosphate
    a coenzyme similar to NAD and present in most living cells but serves as a reductant in different metabolic processes
    nucleic acid
    (biochemistry) any of various macromolecules composed of nucleotide chains that are vital constituents of all living cells
    triphosphopyridine nucleotide
    a coenzyme of several enzymes
    coenzyme Q, ubiquinone
    any of several quinones found in living cells and that function as coenzymes that transfer electrons from one molecule to another in cell respiration
    type of:
    building block, unit
    a single undivided natural thing occurring in the composition of something else
  2. noun
    (nontechnical usage) a tiny piece of anything
    synonyms: atom, corpuscle, mote, particle, speck
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    a relatively small granular particle of a substance
    material resulting from the process of grinding
    a microscopic particle of triglycerides produced in the intestines during digestion; in the bloodstream they release their fatty acids into the blood
    a tiny dark speck made by the excrement of a fly
    identification particle
    a tiny particle of material that can be added to a product to indicate the source of manufacture
    a tiny grain
    (trademark) a microscopic and traceable identification particle used to trace explosives or other hazardous materials or to prevent counterfeiting
    type of:
    material, stuff
    the tangible substance that goes into the makeup of a physical object
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