NCIt definition : An aggregate of two or more atoms in a defined arrangement held together by chemical
bonds.;
Alternative definition : NCI-GLOSS: The smallest particle of a substance that has all of the physical and chemical
properties of that substance. Molecules are made up of one or more atoms. If they
contain more than one atom, the atoms can be the same (an oxygen molecule has two
oxygen atoms) or different (a water molecule has two hydrogen atoms and one oxygen
atom). Biological molecules, such as proteins and DNA, can be made up of many thousands
of atoms.;