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noun, plural: moieties

(general) A half or one of two approximately equal parts of something; an indefinite portion or part or share of the whole.

(chemistry) A half of a molecule; a significant segment, portion or part of a molecule that may include a substructure of the functional group.

(anthropology) One of the two descent groups from an equally divided society; each of the primary subdivisions of kin-related groups of a particular society.


In chemistry, a moiety is originally defined as half of a molecule. For example, benzyl acetate has an acetyl moiety and benzyl alcohol moiety.

Recently, moiety is used synonymously for functional group, which may be erroneous. In the example above, each moiety of benzyl acetate contains a portion of the functional group. Hence, to use moiety to mean a functional group is, therefore, inaccurate in this case.

Moiety is originally a common term in anthropology and archeology to mean the half of a tribal family. An encounter between Elizabeth Bollwerk, an archeology graduate student, and a drug research scientist led to the term's crossover.

Word origin: from the Old French meitiet (French moitié), from Latin medietas “half”, from medius “middle, half”