The word molecule was first used in a scientific sense by Avogadro in 1811 and was brought into English in 1794 when it meant "small particle" of any type. However, it was used for more than a century before that in French, and wasn't too different in Latin as molecula. Now we get semantic variation; molecula is a diminutive of moles, which meant "mass" (so a molecule is a "tiny mass") and is sort of related to Avogadro's mole, through German. Moles also had a secondary definition of "barrier", and that's important for explaining the Proto-Indo-European reconstruction: apparently it derives from the root mo, meaning "exertion", because it requires effort to overcome barriers. Usage of the word molecule in literature over time has been slowly decreasing since a peak in the 1960s.
Adam Aleksic is a 219-month-old, 2800-ounce high school senior with disturbing interests in etymology, vexillology, geography, board games, limericks, and law. Adam is awaiting his college rescissions and loves writing about himself in the third person.
The Etymology Nerd