Molecule (noun)

1. The smallest particle of a substance that retains the chemical properties of that substance and is composed of one or more atoms.
2. A simple or complex structure consisting of a group of atoms bonded together, forming the smallest particle of a chemical compound.

Origin:

Late 19th century: from french molécule, from modern latin molecula 'small unit', diminutive of latin moles 'mass'.

Examples:

1. Water molecules are made up of two hydrogen atoms and one oxygen atom.
2. The scientists studied the molecules in the gas to determine its composition.
3. The new drug targets specific molecules in the cancer cells.
4. The size of a molecule can range from a few to several thousand atoms.
5. The chemical reaction resulted in the formation of new molecules.