A molecule, or the simplest structural unit of a substance that still keeps the properties of that substance, is a scientific word that gets used by the nonscientific, as in "Every single molecule in my body wants that chocolate cake!"

The only problem with molecules really, is that people confuse them with atoms. Here's the thing: a molecule retains the characteristic of the substance it is from, so a water molecule, which is made up of hydrogen and oxygen, is still water, while an atom — one of the tiny units that make up elements — only has the characteristics of its element, not the larger composition. Make sense? No? OK then, just remember a molecule is something really, really small, and an atom is even smaller — since a molecule is composed of atoms!

Definitions of molecule

n (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

n (nontechnical usage) a tiny piece of anything

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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