MCPS refuses to enroll child in 6th grade/middle school who has completed 5th grade

[Anonymous]

If she meant "an extremely small portion" this is not one of the meanings even in the context of physical chemistry. Plus, that usage seems to be specific to chemistry. She didn't seem to be using it to refer to a part of a molecule.

But maybe she just meant "half" or "a portion" and wanted to say that in a colorful way.

http://goldbook.iupac.org/M03968.html

[Anonymous]

Yup, that was my point. She's using it exactly like a bright 9 year old might -- with a desire to show off and with little or no understanding of diction or connotation.

In contemporary usage, when moiety refers to a group of people ("the __ moiety") it's generally in an anthropological context where the group being discussed is part of a social structure that's been organized in a binary way with rules governing how the two halves interact (e.g marriage must be within or external to one's own moiety).

As PP pointed out, the use in chemistry is different, but still flags a substantial component. And I think that chemists generally use the term in ways that characterize the whole molecule before (or soon after) defining the subcomponent -- e.g. a ___ molecule with a ___ moiety or the ___ moiety of a ____ molecule.

There's also a legal use (now rare if not archaic) of a half-share in real property.

[Anonymous]

Aha! Thank you! I was trying to think where I would possibly have read that word and gotten such a strong sense that it meant half. It was in Property!