Pronunciation: (mol'u-kyOOl"),[key] —n. 1. Chem.,Physics.the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound.
2. Chem.a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.
3. any very small particle.