Just ran across that word in my trade journal 'Vacuum Technology and Coating'' which I get monthly.
The article is X-Ray photoelectron spectroscopy and auger electron spectroscopy, comparison and basic principles by Wang and Linford, contributing editors.
The context:
These (perturbutions of atoms as the result of electrons slamming into them, my words) are often observed in organic molecules that contain aromatic (benzene-like) moieties.
So Moiety or moieties means parts of a larger molecule, like benzene rings that are assembled together within a larger assembly of molecules, so moiety can be thought of as sub-assemblies of a larger part.
It is also used in anthropology to describe separation of a main group of people like the caste system in India or the Aborigines in Australia.