Molecule - (n.) One of the very small invisible particles of which all
matter is supposed to consist.
Molecule - (n.) The smallest part of any substance which possesses the
characteristic properties and qualities of that substance, and which
can exist alone in a free state.
Molecule - (n.) A group of atoms so united and combined by chemical
affinity that they form a complete, integrated whole, being the
smallest portion of any particular compound that can exist in a free
state; as, a molecule of water consists of two atoms of hydrogen and
one of oxygen. Cf. Atom.