mendacium

Mendacium is a Latin noun meaning a lie, falsehood, or deception. It refers to an utterance or act intended to mislead, or to the general concept of deceit. In classical Latin, mendacium could denote both a single false statement and deceit more broadly, including falsehoods told for various ends. The word is neuter and belongs to the second declension; its genitive is mendacii, and its accusative is mendacium.

Mendacium derives from the adjective mendax, mendacis, “lying, deceitful,” from which English mendacious and mendacity ultimately descend. The noun mendacium appears in Latin authors from the late Republic through late antiquity and in medieval Latin, where it described false statements in moral, rhetorical, or legal contexts.

In English-language scholarship, mendacium is encountered mainly in discussions of Latin language or in translations in historical texts. The related English terms mendacity (habitual lying or falsehood) and mendacious (false or lying) are cognate derivatives.