mol·e·cule 
(mŏlĭ-kyl′)
(mŏlĭ-kyl′)n.
1. The smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms; a group of like or different atoms held together by chemical forces.
2. A small particle; a tiny bit.
[French molécule, from New Latin mōlēcula, diminutive of Latin mōlēs, mass.]